RCH - Glad to see you here! Like Bill mentioned, the non-sound version of the Railpro modules are priced lower and can be useful for converting larger fleets.
However, if you're like me, I prefer to have sound in all my locomotives....for me it's part of the whole modeling thing. I go to great lengths to replicate details and weathering, and I try to do the same with sound as far as I'm able. The sound-equipped modules are more expensive.
There are other Railpro users in the same boat as you. Lots of locos and don't want to change them all over. My answer to that is don't worry about changing all of them. Pick a few that you typically run in consists (since that's where you'll really see Railpro's benefits) and convert those. Continue with DCC in the others and change them over as you feel you need to. There's no reason to change all of them at once, and you may even find a healthy balance between Railpro-equipped locos and DCC-equipped locos and leave it there. I'll be honest though, once you start operating with Railpro you'll find yourself using DCC less and less. That's what happened to me. Any of my locos that had DCC ended up sitting in the box until I got around to switching them over.
I've said it before, and I'll say it again....in my opinion the only thing DCC really has going for it is the sound. Everything else is like slitting your wrists and doing push-ups in salt water. I'll take Railpro's ease of operation and fun any day, even if Railpro's sound is not yet up to current DCC standards.
-Kevin
