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

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.

Tomcy6, actually Stereophile measured 130, 195, 332 Watts into 8, 4, 2 Ohms respectively, before clipping (as defined by 1% THD). If one were to use the 2 Ohm measure and work up, it would start to look more like an 80 Watt high current Class AB amp. Since the OP speakers don't drop to 2 Ohms, I thought we could be a little more generous with a 100 Watt high current Class AB designation. All in all, still rather close to Thiel's minimum recommended power.

I had a Thiel 2.4SE which I traded up for a 3.7

I've heard it with different combinations of Pre and Power before.

For my money, I found the Bel Canto Pre3 and REF500M to be a good pairing. I found the Bel Canto

If the budget could stretch further, I'd use a tube preamp which adds lushness and some 3dimensionality. I've heard it partner well with LAMM preamps and also with my Audio Research Ref5 and now 5SE. I am not a fan of overly warm and slow music reproduction and like dynamics so these two have been a great combination for me when I use SS power amps.

Unsound, I stand corrected.

Nothing personal, just for the record.:-)