I have an RMC-1 driving an XPA Gen3 with 10 total channels (4 single and 3 dual channel cards). I'm using the 4 singles for side and rear surround, and the others for ATMOS.
Just wanted to pass along some info that might help others. I didn't have enough XLR cables handy so I used an Emotiva XLR-to-RCA adapter to run the processor into the rear surround RCA inputs (using high quality RCA cables), and flipped the switch accordingly. It caused low-level but noticeable hum in the speakers. Replaced those cables with XLR's and the hum went away.