Many sound decoders, especially the older ones, don't work well with the standard programming track signals.
For QSI decoders a programming track booster is recommended. I cannot tell you if that will work with an MRC system. Another solution is the Digitrax PR3/PR4, which connects between a program track and your computer, which can program the CVs.
https://dccwiki.com/Programming_Track#Programming_Track_Boosters
You will need software such as JMRI on your computer if you go the PR3/PR4 route.
What should one use to program an older QSI Quantum decoder? As I run MRC the QSI decoder won't program on the program track, only on the main...The decoder I am running requires programming as its consisted with another loco that just has a standard Digitrax Decoder .The digitrax decoder is easier to reprogram and I have changed many settings on it to try and consist the two but the QSI is fighting the digitrax especially at startup...