What tube pre-amps pair well with Pass amps?

I have to disagree with Atmasphere on two points:
1. I have a fully balanced Pass Labs XA60.5. The cable does make a difference.
2. I have two high quality Cary preamps. Cary SLP-98P Formula 1 mod, which is single ended. Cary SLP-05, which is fully balanced, but not upgraded. The single ended preamp sounds better with the Pass than the balanced in my case. That is why I am upgrading the SLP-05, for better SQ.
The bottom line is that preamp quality is more important than using the amp in the balanced mode.
Btw, make sure that if you use the Pass Labs in single ended mode, to insert the shorting jumpers, so that the unused half does not introduce noise.

One caveat to my points.
My preamps are very close to the Pass amps; so the interconnects are short. With a longer interconnect run, the balanced connections may possibly be superior.

I have Pass Labs XA60.5 amps. My preamps are both Cary Audio - SLP-05 and SLP-98P F1 version. The modified SLP-98P sounds a tad better, so the SLP-05 is off to Cary for the Ultimate Upgrade. It should sound as good or better than the 98P when I get it back. The 05 has more features that I like - HT bypass, balanced operation, no phono.