Anyone knows the Classe CA-401?

I'd suggest the Spectron Audio Musician III SE Mk2. It is a very musical amp with tremendous headroom and extention and almost 'tube-like' but without the 'veil'. It will drive any and the most demanding speakers including your Thiels.

Classe equipment was used to demo with Thiel speakers at a lot of audio shows that I had attended in late 1990s and early 2000s. Can't remember exactly how they sound, but I believe there is some synergy there.

If you are using the X1, why not go with a X250.5 or X350.5. I had lived with a pair of Thiel 3.6 for over 10 years. I had powered them with a Mark Levinson #333 most of that time. Due to some reliability issues, I had replaced the amp with an X350.5 last year. Out of the box, the X350.5 sounded amazingly good. I was dumbfounded as I had thought with my system that I had pretty much "got the most out of" these Thiels. With the Pass, I got deeper and more controlled bass, more extension in the treble. The soundstage extended behind the speakers and also wider/bigger. The the midrange had that special sparkle that you get from tube amps.

Up to that point, I had been contemplating upgrading my speakers for over two years. After I inserted the X350.5 into the system. I seriously thought about keeping the Thiels. But then, where's the fun if you don't play with more toys. Currently, I have a pair of Verity Parsifal Encores. As good as the Thiels were, I am very happy with these.

FrankC

I owned the CA-400 for a few years which drove Martin Logan Quest speakers. Nice amp, I really liked it a lot; a real brute, never ran out of steam, very controlled bass. Although not a tube sound, I thought the midrange and top were quite good. Very well made. Not sure what the difference in the 401 is.