I believe he's trying to say both devices should be plugged in to the same power strip so that the grounds are at the same level. Don't seperate the units by a bunch of cable.

The AMC supplies 12V to power an IR receiver, you don't have to worry about that as the MRF has it's own power. If AMC supplied enough power on that +12V you could potentially power the MRF with it and avoid the common ground issue, but just ignore it for now.

Shield is ground. Black is data. Turn down an emitter on the MRF to as low as it can go. Wire it up. Cross your fingers, and see if it works.