It appears to have possibly been a "pig in a poke."

https://en.m.wikipedia.org/wiki/Pig_in_a_poke

Verily, verily, I say unto thee. Bewarest thou of used model locomotives, lest thee encounter the dreaded "pig in a poke"

There's a Digitraxx io forum you can ask these questions on.

https://groups.io/g/Digitrax-Users

I know all about the pre-retirement Model Railroad roster bulk-up purchasing. While I had an income to support it all. I built my roster of steam engines up to well over 60, I'd have to count to be certain.  Some of them will probably hardly ever run at all, but I wanted them for so long, I got them anyway.

To make a long story short, you are basically glueing the spilt hub back on with Loctite. Right?

I run my my layout with the NCE Procab command station connected to the track with two wires. One for each rail.  That's it! All I need! I love simplicity! If I wanted to do wiring, I would have built a Heathkit radio kit! That is, if they still have them!

I am running wireless, so the cabs answer to an antenna that is wired into the command station, rather than being tethered into a buss to the track.

That is it!  All of it! From beginning of "wiring" to operation, 10 minutes! Or less!

The gurus and gods in Milwaukee have decreed that all layouts need a buss wire system for each track, with the layout broken up into isolated electrical zones  each with a circuit breaker. And feeders from the bus to the rail, every 3 feet or so.

In most cases, all of this is overkill for people who are obsessed with soldering. People that would solder a bing cherry onto an ice cream sundae if they could figure out how to do it.

I say that, while on larger layouts, such complication may be necessary, on most of the small home layouts most people have, all of that is ridiculous overkill.  My friend up in New York has wasted six months trying to wire a 4 x 8 layout with all the stuff discussed above.  When I finally heard about it, I told him dude, stop it, you don't need all that, just hook it up and run your trains.

Mercy sakes, Quentin, I do declare! (the way my Mississippi grandma used to talk.) all this talk about the DigiTraxx thingy is fine. Until you want to change a setting. Like the whistle. If you're really into whistles like me.  Tsunami2-2 has 90. Of course I don't like all of them, but there's about a dozen of them I do. Five chimes and six chimes, I don't care for the three chimes or the hooters. I change the whistle on almost every engine at least once in an evening of operation, sometimes more. Even with 90 whistles in that decoder, there's still several prototype whistles I like that aren't in there. Like a real southern pacific six chime. Although there's three so-called ones on there already, they are all imposters. Or one of the little cast iron 6-inch-high five chime screamers that were on almost all of the T&NO and MP engines.

Or, second reason to want a more advanced system, if you want to give a locomotive a real address other than a single digit, and have more than 10 engines you want to assign addresses to.

I understand that smaller reach operating systems suit some folks well. But when I first fired up my NCE wireless pro cab 15 years ago, I knew there was no going back.

Yes. Flat River was on the very western end of the Illinois side of the Missouri-Illinois.

I have Charlie Duckworth's M-I book and have molecularly read it cover to cover.  It definitely is my kind of Railroad.

My friend used to see M.I. Box cars with the Missouri Pacific Buzzsaw herald in the yard back home in the early 60s. He thought that they had forgotten to finish painting the "P" on those cars.😂😂

There are several great photographs around the M – I in Flat River in the 20s. There was also an electric interurban railway in that area that is covered in his book some. One of the photos has a Pacific going around a curve in front of the depot, with overhead catenary wire for the electric operation above the track.

Scroll down to the 2-8-0's.  Look at the 1019 and the 1025.  These little ex-Frisco engines are right up your alley, and they are some of the very ones that ran on the branchline back home that I saw as a child.  The three swing bridges on the branch could take nothing larger.

http://www.trainweb.org/screamingeagle/loco_steam.html

You can add Pacifics to your short line steam locomotive list.

U S Sugar at one time ran four ex-FEC Pacifics, 3 of them survive today.

https://www.ussugar.com/u-s-sugar-steam-locomotive-no-148-hauls-sugarcane-train-to-mill-ending-harvest-season-new-sugar-express-launched/

And, this article is out of date, they're in the process of restoring the engine to operation.

https://www.trains.com/trn/news-reviews/news-wire/u-s-sugar-interested-in-acquiring-second-steam-locomotive/

After learning about all of this, I immediately put my USRA Pacific at work on the locals.

The New York Central ran Pacifics on some local and branchline freights quite a bit too.

You should read up on the Missouri-Illinois. I believe you would like it. A 110 mile short line that ran on both sides of the Mississippi river with a car ferry connecting them. In relatively modern times it was run by the Missouri Pacific, and the engines were lettered just like MP engines, except instead of Missouri Pacific up in the coal board, the tender said Missouri-Illinois. Plus they ran MP equipment a lot of times. They ran doodlebugs too.

http://laiben.com/wordpress1/about/

You really need to include the decapod in your list of short line engines. That engine was smaller than many consolidations with an extra set of drivers to spread the weight down over poor branch line and short line track. 
I have every modern 4–4–0 and 4–6–0 that Bachmann ever offered. but I run nearly all my locals with my decapods. 

Plus. About that Bachmann consolidation. While it is definitely a large engine, it is astonishingly close in profile and detail to a Missouri pacific spot – class 2-8–0, numbers 1–173 and general Missouri Pacific practice.  I think they are perfectly acceptable to run down a branch line.  Both those engine styles run regularly down my branch. In fact, my trains have gotten longer, almost to 10 cars a lot of the time, very long heavy drags on my little Railroad.

I remember in high school going nutsy-cuckoo over a NWSL logging mic for sale at an NMRA regional meat. Of course, I couldn't afford it, but I never forgot about it. Those things ran all over East Texas on various logging roads not too terribly far from my boyhood home. And I always wanted one. I doubt if anyone ever brings one out in plastic, they are just too specialized and and small of an engine when everybody wants Big Boys and northerns because they've seen them on excursion trains. I already had the Wabash mogul and the ma & pa 10 wheeler, the same locomotive is Bachmann's present low boiler 10 wheeler.

I myself would like to see a plastic version of Varney's Old Lady consolidation, a beautifully proportioned small engine that I always liked, but never had.

When I was a kid, I didn't know all about the big, bad world and all of its problems. I only knew that the sun was shining in my world, it was a beautiful day, and the only responsibility I had was to play.

Sometimes with me, it's sort of like that with this decoder business. I still remember the first DCC/sound locomotive I bought, a Soundtraxx sound on board Bachmann 2-8-0 way back in 2007. Plus one of the first run decapods with the same decoder. I bought an EZ because I was intimidated by DCC and was told that the EZ command was the easiest way to get started it, for $75 or so with the time. I didn't know how to change any CVs and was happy just running the engines back-and-forth on a simple run around track deal I had on a 1x8 board, blowing the whistle and ringing the bell. It took me over a year to get the confidence to become involved with a more advanced system. But I have to say, I probably had more fun than today with those two engines just the way they came from the factory.

It only solves sound quality issues at higher volumes. It doesn't allow adjusting of all the other individual CVs, for the various sounds.  To do that you need some device capable of actually changing the cv volumes to suit.

I myself like using the programming on the main option in a DCC system like NCE wireless pro cab that I've been using for about 15 years now. You can actually raise the whistle up and down while the engine is running, to see how well it realistically covers up all the other sounds.  Some of the old soundtraxx sound-on-board products that were factory installed in. Bachmann engines had very anemic whistles. According to my friend who works out there, Tsunami2-2 has a much better amplifier and you can't turn the whistles up all the way without distortion. After programming a few engines with tsunami 2–2, you start learning the limitations.

Lets you keep the basic EZ command. But. After getting a more advanced wireless DCC system, there is no going back to the EZ command. I gave it to a kid who was just getting started in model railroading.

Still ..... QSI is gone, and any decoder made today will far surpass any of those early sound units.