You do not need to change to MTS, just get the engine upgraded to digital and have MTS compatibility.
The MTS decoders do not have sound and for just $25 dollars more you can get decoders that have motor/light/sound/and puffing smoke control.
There are many places to get this done and where I work, Train-Li is one.
Which MTS system do you have? All of them are restricted to 14 speed steps and 5 amps. And some are serial only.