I've "played" with the engines with the decoders, and thought I'd at least post the results I have in hand, until I find my &*(%&^%^ camera.
First, I found the volume level increased by pointing the speaker at the frame of the locomotive, kind of the opposite what I expected. It's even better if you put a small piece of electrical tape over the frame, and point the speaker toward the tape. One of the three takes a while to start moving, the other two move out very smartly. So smartly, I've had to configure the acceleration and deceleration rates for them. Now the sound of the prime movers spools up, and the unit starts moving. Before I did this, the jackrabbit took off before the engine sound changed speed or tone.
Next, I (gasp!) mounted one of the three in an AC4400CW, and configured the prime mover sound for the 4 cycle. It's a little goofy sounding, as it chugs, then smooths out, then chugs again as the throttle is advanced. There isn't any steady "chop-chop-chop-chop" sound you would expect. I also had to perform surgery on the AC4400CW, albeit minor surgery. One of the electronic components sticks up a bit higher on that particular board than the other three, and was holding the body shell up in the rear. After careful examination, I removed the radiator grill, and cut away the part of the body shell that was contacting the decoder. This allowed the piece to extend up through the shell, and you can't see it when you put the radiator grill back on. Naturally, it was the only one of the bunch with this part on it, any of the others would have dropped in without modification.
These three have now been in service on my layout for several weeks without incident, and it's pretty cool to have two SD70's and a GE go rumbling by.