As great as the DCS is, I've made the decision to pull out all PS2 modules out of my MTH diesels and replace with DCC/Sound. It's not hard, and often quite therapeutic. We have a lot of great choices now in O Scale for DCC/Sound. Much more than we had even 2 years ago. Depending on the numbers of MTH PS2 diesels you have, you might consider the converting them to DCC. There are plenty of guys who buy the PS2 modules.
IMO, I believe the best sound decoders are
1. WOWSound (larger scale version coming out VERY soon)
2. Soundtraxx Econami decoder (ECO-400)
3. ESU Loksound L Select v4
Not even counting the smaller decoders, Tsunami, etc...
We have some killer motor/function decoders too if sound isn't a big deal...
TCS G8 (By far my favorite), but also like the Digitrax DH465, NCE408