RCA to pass X150?

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.

Scb6 is right on. Also, I seem to remember something about the Hovland and Pass having a very poor impedance match. A while ago I posted a thread on impedance matching. You might want to check it out.

Thanks guys. The output impedance is quoted at 2K Ohm and the input for pass is 22K Ohm. On these numbers, it would be an OK match. However, stereophile tests indicated output imped. rise to 4700 Ohm at 20 Hz. It is less than ideal. I am going to see how it works out. I may purchase an X1 to experiment with but that means changing all connections to XLR. Any good tube pre that works with pass?

I love my sonic frontiers line-3 with my x-350. Its very neutral, not a warm preamp though.