best tube preamp under a 1000 for B&K 200 sonatas?

I could be mistaken, but I seem to remember that the B&K M200's having a fair low input impedance of 22K(?) Ohms. I had a friend use a Sonic Frontiers Line 3 with 4 factory matched B&K M200's with balanced inputs with great success some years ago. But I doubt you'll find that pre for a grand or less. Do your B&K M200's have balanced inputs?

Unsound, yes they do have the balances inputz.

Hello,
I see a TAD 150 Signature posted on Agon. I owned one 4 years ago. A very nice sounding tube preamp for its price point. Has no short comings really - just sounds right. Has remote, only uses (2) tubes so tube rolling is not too costly. It has a phono section but to be honest it's not that good. The value here is in the line stage.
If you could get it for $775 I'd jump on it.

I'd be careful - that TAD 150 isn't a signature (near as I can tell based on the pictures). So $775 may not be a "jump on it" value. That said, I have a TAD 150 sig that I have used with my B&K M200's and it worked great. I have been driving my M200's for the past 3+ years though with a Musical Fidelity Nuvista preamp. The Nuvista isn't a traditional tube amp - it uses miniature "Nuvistors" which are more tube than they are transistor, but they look like a transistor. It's a great preamp and it's a great combination. They can be found used from time to time for ~$1000 but since there were only 500 made they aren't common.

+1 Quicksilver, < 300 ohms output
Audible Illusions line1, 2 ~1600 ohms output
Jolida Fusion has both RCA and balanced outs, if one comes up used,

I am driving a BEL 1001 MK5 having 22K ohms input with Aubilbe Illsions 3a with no problem, 2M interconnects.

I could be mistaken, but I seem to remember that the B&K M200's having a fair low input impedance of 22K(?) Ohms.

you're very close - the published spec is 24.3 Kohms