Here’s the part that concerns me about this amp possibly not having a "true" differential input, despite earlier verbiage:
If a balanced connection cannot be used, note that the amp cannot be driven to full power from a 2-volt single-ended output, the limit of most receivers. You leave half the power on the table.
Maybe it’s a real differential input and the amp simply has a very low sensitivity that requires more than 2 Volts to hit its full rated power output (i.e. use a single ended preamp with some gain, or a DAC with some extra gain, and you’re golden). Or maybe it actually DOESN’T have a differential input, and half of the amp’s 4 phases will be sitting at 0 whenever you use RCA-to-XLR adapters.
We’re trying to derive precise meaning from their verbiage, which could be either partially erroneous or easily misinterpreted. I’d contact the company for clarification.