The volume on my DD40 horn is very weak. What CV # can up the volume?

I'm sure this question was answered before, but I couldn't find the answer. Have 2 4-4-0s 1 goes forward the other backward. Would like to change polarity.

Yes again to your ? This is called Double Heading and is very common in Model Railroading as it is 7 was in railroading. The previous answer of you'll need more power, as now your powering 2 motors. 

I'm looking for as sound set-up for my HO 3-truck shay. In my search I found only 2 postings 1 from '07 & 1 from '08.
There must be more on this, doers anybody know of a sound system to put into an HO Shay.
Thanks & I'm new to this form