What tube pre-amps pair well with Pass amps?

@cakids   +1 !

The bottom line is that preamp quality is more important than using the amp in the balanced mode.

@cakids
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...

Last year when I was demoing different amps again, I asked Nelson about my own Cary SLP-98/F1 tube preamp pairing with a Pass .5 or .8 amp. He shared having many customers running them already. Guess it’s true :). A buddy with the XA-25 amp also tried with his own SLP98 preamp and liked the pairing a lot. We agreed it was not quite like his strapped triode tube amp, but really nice and musical!

May I respectfully ask for the names of some pre-amps that meet AES48?

Well ours do of course. Also Backert Labs, if you get the version with an output transformer to do the balanced output. Most preamps that use an output transformer in that manner should be able to support the standard- and it won't matter if the internal circuit is balanced or not.

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.

This is actually a really good example of what I was talking about. The Cary does not support AES48- any preamp that has RCA and XLR outputs, and does not need a switch to use one or the other, very likely does not support the standard, and so you will hear differences between cables that can be pretty profound.

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.

The benefit of balanced operation really does not have much to do with the length of the cable. The benefit can be there even if the cable is only 6 inches.

I am using the Pass Labs XA-60.8 amps with the Pass Labs XP-22 preamp in balanced mode and I can only say the musical presentation is outstanding in every way. It is very musical and not in the least anemic or lifeless. I have not heard any other Pass Labs preamps, but what I am hearing now is the best I have ever had in my system. 

Pass Labs whether due to technological or marketing reasons promotes their “super symmetry” as a selling point. This might be best used in balanced mode. Some of the Pass Labs amps have a somewhat low input impedance.  If wanting to use tubes, I suggest considering the Atmasphere and Sonic Frontiers pres.

@unsound If you're curious, here's an article where Nelson explains what the term actually means... https://www.passdiy.com/project/articles/super-symmetric-amplification