Have opportunity to buy BHK 300's or Pass Labs 250.8 for my Thiel 3.7's- thoughts??

Wish I could comment on the Pass Labs gear, as it certainly enjoys a great reputation, but, alas, I have never had it in my system (well, an Aleph 0 back in the 90's!).  I can vouch for the PS Audio BHK 300 mono's, which I have been using for ~2 years now.  They are very nice amps, IME, and they run my TAD CR-1's beautifully.  I think you cannot go wrong with them (and the 6922 tube input for system "tuning" is a very nice feature).  Just my 2 cents.

Pass Labs, no question.

By all accounts Bascom King did a masterful job with the BHK amplifiers. Pass Labs has earned an esteemed reputation. I’d audition both of them at home . I don’t agree that Pass is a no brainer choice compared to the BHK. You must listen and then decide preference. 
Charles

pgastone

After you figure out your power amp situation, please join us over on the Thiel Owners thread.  Happy Listening!