Thiel 3.6, what will drive them best?

I was curious about the B&K M200, so I did a quick Google search. This is for information only from a Soundstage review of Thiel CS2.3:

When the CS2.3s were first installed, I drove them with some aging B&K M200 mono amplifiers, rated at 200 watts each but certainly not current powerhouses. The performance was certainly presentable, but a relative softness in the bass and a sense of "topping out" in the dynamics left a nagging feeling. Inserting the Bryston 4B-ST amplifier (review in the works) dramatically changed the presentation. Dynamics, coherency and imaging all improved under its control.

This quote is from a Stereophile interview:

Two amplifiers that I recently wrote about, the B&K M-200 vs the Adcom GFA-565 monoblocks—both of which I liked—were a very good example of this frustration. The B&Ks had a sweet sound and perhaps did a better job at presenting musical timbres. The Adcoms, however, were much more open and more transparent; they let in more detail; and they allowed the differences in recordings to show through.

So, certainly the B&K M200 might be worth a try, especially considering they are available used for under $500.

Maybe buy them and order a pair of the EVS100M to have both in-house at the same time.

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.