Peteski,
Yes, I have considered a cheap-as-possible option. Since this is going to be an A-B-B-A setup that I probably won't break, I may just put sound in 1 unit, probably one of the B's, and non-sound decoders in the rest, so that I have a horn and bell.
I might even be able to get away with no frame milling if I do that. If so, then maybe sound in both B units.
Because my plan for these (as of now, at least) is run-through from staging to staging, I would be using the horn and maybe the bell, but not really the startup and shutdown sounds.
However, it would be nice to have some other sounds besides "electric razor" as they go by, even with the electric razor sounds mixed in. And I am thinking that "quadraphonic" sound from speakers in all 4 units would be the best way to "cover" the unwanted sounds.
Another issue is whether I can get the ESU Nano on the 24 pin connector into these units without any milling. Being able to swap out the decoder without soldering seems like a plus with the current ESU quality problems. It looks to me like that will require a bit of milling, so, I need to decide how much effort I really want to put into these units. With some effort, I think I could make them really nice, except for the razor noise.