Thiel 3.6, what will drive them best?

Unfortunatley, I think the sub $1000 budget is tough for the 3.6's.
As a long term Thiel owner, ther's no substitute for adequate current. The quality output devices and power supplies to provide adequate current aren't cheap to build. I'm afraid you'll be disappointed with amps that don't perform the obligatory tasks in that large room.
I'd recommend the perenial great match for Thiels of this vintage.....Classe amps. The are well built, provide lots of current and sonicaly are a great match for the Thiels.

In this situation, cheap is expensive because you'll have to replace an inadequate amplifier. Happliy, Good Classe amps are generally available, and versions prior to the current line-up can be had at fair prices.
Generally, if you speak to the customer service folks at Thiel, they'll advise against the matching of Krell and Thiels of this vintage. Good Luck

Tvad, interesting reviews that I haven't seen previously. One comment I find curious

aging B&K M200 mono amplifiers, rated at 200 watts each but certainly not current powerhouses.

. B&K rates them as 150 amps peak-peak, which is the basis for my statement. The biggest challenge I've presented them is Totem Mani-2s, which they drive very nicely, and I've no other basis for supporting refuting the rating. I don't presume B&K's rating is necessarily accurate, but it's has me wondering what the reviewer's baseline is causing him to make this statement.

Another amp worth considering in this price range is the Parasound HCA2200. Either the mkI or mkII can be found used in the $600-800 range. I have the mkI which I liked a lot, though I replaced it with a pair of M200's which I preferred. I think the differences are in the personal preference range and some my like the HCA2200 just as well as or better.

What qualities made you prefer the M200's over the HCA2200?

Thank you,

Ron

Ron,I have heard the Stratos Odyssey combination and Thiel
five years ago,the result is so musical,they are match made in heaven,the tonal balance is so hard to forget,If I did not end up with Diapason,I will buy 3.6Thiel.Because I do own the monoblock extreme odyssey.Since then I end up
using art audio concierto amp.I think its worth doubling
your budget,if you can.

Unfortunately IMO you will not find anything in that price range to drive them to their full potential as you put it. Thiels really need both high power and high quality power to be great. If budget is an issue then quality over quantity is better. But in your price range either one is going to be very difficult to achieve.