I believe the RCA to XLR adapters simply make it fit the XLR input. It does not turn the RCA signal into a true differential signal. The Pass definitely sounds better run in balanced mode but I imagine it would sound fine with your preamps.
The Pass amps come with a small jumper wire that is inserted in the XLR input to short the minus to the ground pin when using the RCA input. It does the same thing an external RCA to XLR adapter would do.
The Pass amps come with a small jumper wire that is inserted in the XLR input to short the minus to the ground pin when using the RCA input. It does the same thing an external RCA to XLR adapter would do.