Tube Amplifier for Thiel

Using a tube preamp with ss power amps does give you some sense of "tube sound" but the amps are even more important in that respect. Most of the time I had the Classe amp, I used an ARC LS-2. Probably not the best match but that's what it was.

That room might be a little tight for the 3.6's. Long wall placement might be worth considering, do use some absorptive treatment behind the listening position if you do.
The bad news is that the 3.6's impedance level is below 3 Ohms most of the time. The good news is that the phase angle isn't too harsh. Still, not a typically a good load for most tube amps, or even many ss amps for that matter. This speaker demands an amp with real grunt, and don't skimp on the power. Such amps exist, even within your budget, but if you intend on using a tube pre, then you have to consider the input impedance and voltage sensitivity for full output of the amp. Many tube pres have a rather high output impedance for the typically low input impedance of most ss amps, and many tube pres have a rather high output voltage for the high sensitivity of many ss amps, rendering the volume control of such a pre with limited range. It can be done, and done well, but one needs to take in all of the above considerations, not to mention how it all actually sounds too boot.
Finding a suitable tube amp for these speakers becomes costly. So costly that one should seriously consider if the money spent would reap better sound with higher level Thiels and ss amps.

Conrad Johnson.

Conrad Johnson is a great match. These speakers need POWER!

Happy Listening!

I have used Thiel speakers for many years, in many different systems. They need power, but much more importantly, the need solid state or high powered tube amplifiers that can provide substantial amounts of CURRENT into low impedance loads.
Three good choices that are generally in your budget are the MCCormack DNA amplifiers (like the DNA one), Classe amps from a few years ago, and the previously stated Conrad Johnson solid state amps like the MF 2500.
There are a number of others as well.
I'd use a warm sounding tube preamp that has good impedance match with the amp. Select the Amp first, then the preamp. The Theil 3.6 is capable of beautiful music if fed properly.