Thiel 3.6, what will drive them best?

A pair of Bryston 7B-STs will drive them nicely and can be gotten for relatively little money. Some think that that earlier model actually sounds better than the current one.

An inexpensive choice is Class D amplification.

something with lots of power

Look for a used Classe DR-9 I can't think of a better amp built and sound wise and right in your budget. I would also think that a used pair of B&KM200 mono amps can be had for around 500.00 or less and are wonderful.

I used to play mine with a very updated Audio Research VT-60, which probably did not control the bass like a good SS amp would.

At the sub $1k mark, I suggest something like a Belles 150A Hotrod, OCM 200 or 500. Some of the updated Hafler 500 amps sound very good too. You can find all of those amps at less than $1k. Another line of amps to consider are the older Coda amps. Sometimes you can find a nice Coda 10 or 10.5 in the price range you are looking for. They are very sweet sounding and can nearly drive a short, so the Thiels impedance issues should not cause them to sweat. I am not a big Krell fan because of all the inherent buzzing ground loops that they seem to have had each time I owned one, however I have heard good things about the Krell KST-100. Some have said it is more musical than a lot of the KSA's and it is Class A/B so it won't eat itself like the KSA's can do.

I hope this helps.