Upgrade From DCC to DCC_w_Sound?

[Chuck_S]

Hi All --

I'm assuming I can fit the same Economi decoder that's in my pair of 2-8-0 steamers that came with sound in the tender of my 4-6-0 DCC (item 51458 lacks sound) tender but don't know (1) how to open either tender nor (2) what decoder and speaker should go in.  Looks easy but without Xray vision I need help.

Assistance appreciated.   

-- Chuck

Added information:  Decoder Pro indicates the decoder in the tender is a Bachman EZ Command decoder so it's pretty old.  I can get the tender shell off but haven't messed with the boards (plural) or wiring.  Would be nice to find a sound decoder that fits.  I popped the shell off one of my 2-8-0 locos but can't find the information for what decoder is in there.  Tender shells are identical.