I can remove vocals but can't figure out how to to do the reverse
In MMM 16 Premium I use two keys:
Ctrl + B =Reverse
Put cursor on the object you want to reverse and use the above command. I hope the above command should work in MMM MX too.
Sorry, but it can't be done. As it's often been said, you can't remove the eggs after the cake's been baked.
You can reduce their influence with filtering, but that will also affect the vocals. You can't remove them completely unless the vocals and instuments are NEVER sounding (playing) at the same time. In that case, you could essentially delete the instruments in the Music Editor. But, what are the odds of that?
The best way is if you had access to the ORIGINAL multi-track recordings, but getting a hold of those is EXTREMELY unlikely.
nihon94 is talking about reversing the object so that it plays "backwards".