if your sub does not have a XLR input, using a XLR to RCA cable you will not benefit from the balanced design of the XLR connection.

I would use the RCA to RCA in this occasion because you signal would be going through less circuitry.
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5 x R&D Audio Monitor 2s
1 x R&D Audio Subwoofer 2
1 x Bryston 4B
2 x Bryston 3B
Denon 4308ci
Oppo 970HD
Belken PureAV PF60