A really interesting topic.
I have three PS-1 (?) MTH AS-616 powered units. I really want to keep the sound; to my recollection they sound like Baldwins, not ALCO or EMD prime movers which is what Rail Sounds offers. As a TMCC partisan I really don't want to modify them to PS-3 (and have Baldwin sound), plus there's the cost.
If "we" can solve the PS-1 -to-TMCC issue, perhaps the next step is Dallee, who offer quite an interesting range of sound files.