With one exception, I do not have dummies on my late 40s layout. Everything has power AND sound. My one exception is a B unit with sound only. This results in very few of my upgraded TMCC diesels being able to run together. Most have noticeably different speeds at the same speed step.
This topic has got me interested in running two or all three of my RailKing Scale DCS switchers together. They are an EMD SW-1, a FM H10-44, and a Baldwin VO-1000 (yes, I know early Baldwins did not MU with other brands). Not sure what I'll pull but it should be fun.
I do have three DCS road engines in bicentennial schemes I have only used as helpers with my DCS GS4 AFT steamer pulling my AFT cars. Maybe next 4th of July when I bring them out I'll try running them together.