Pre-amp suggestions for Thiel 2.4/Pass Labs XA30.5

Shsohis, despite it's (confusing?) nomenclature and marketed specs, the Pass Labs XA30.5 behaves more like a very high biased 100 Watt high current Class AB amp than a 30 Watt limited Class A amp. While perhaps at minimum power needs of the Thiels, it should be adequate in a smaller room and/or with less ultimate volume requirements, and sound quite nice indeed. Others might feel the need for more power with these speakers.
Cal3713, sorry this has gone so off topic, but I hope you can understand that on some level it was bound to happen, and with the best of intentions.

Ha! It is funny to see people's reactions. The amp does, for example, easily best the Classe, as it should given the quality and price difference. Also, unless I'm mistaken, simply watching the front current meter should provide a pretty good indicator of how much difficulty the 30.5 is having driving the speakers. As I've said repeatedly, I only leave class A for 5 - 10 % of my listening.

I don't take that much stock in the meters. In fact, I wish they would do away with them, and lower the prices accordingly. Keep in mind when you start to go out of Class A, and the volume demands more power, the power needs tends to increase exponentially, and rather fast too.

The Pass is marketed as a 30 watt Class A amp. However, it outputs 150 watts into 8 ohms and 300 watts into 4 ohms in class B. So the XA-30.5 could be labelled a 150 watt into 8 ohm Class A/B amplifier with a very high Class A bias. Read the Stereophile review of this amp if you are still not sure about this. Also consider that Nelson Pass rates his amps conservatively.

I have made a couple of preamp suggestions. I think that you would want a c-j Premier LS17 Mk II or newer, if you go c-j.

Their CT preamps use the 6H30 tube which some people don't like as much as the 6922 which c-j returned to in their most recent ET line.

Some people do like the less tubey sounding 6H30 though. If you like detail the 6H30 might be for you, with the loss of some warmth.

I would just again suggest that you get a high gain preamp in order to make it easier for your system to acheive higher volume levels so that you eliminate any concerns about the XA-30.5's suitability for your speakers.

One more thing, the XA-30.5 has a rather low 20Kohm input impedance on its single ended inputs (30Kohm balanced) so you want to keep the output impedance of your preamp below 2 Kohms single ended and 3 Kohms balanced.

Manufacturers seem to rate output impedances as an average like speaker makers do, 8 ohm average or 4 ohm average impedance. Their speaker impedances often dip below this average though and preamp output impedances often go above the rated number. So it's best to find a review that measures output impedance of a preamp to be sure what you're getting.