Fex,
I am not that well informed on current ETS production, but it looks as though the latest higher end steam locos can be ordered in a 3R version [ high flange, center pickup ] with factory DCC that includes sound. Earlier production ETS locos used their own sound system which required I believe their proprietary power supply to give the required wave form. I think a visit to their showroom, if your schedule permits that, would give you the best solutions depending on the locos in question -- they always seemed to me to be a very customer-friendly, accommodating company.
Of course, going to 2R would give you a wider range of motive power and rolling stock from other manufacturers. Have fun whatever you do !
Best, SZ
