Which Threshold amp to buy???

My Threshold experiences are with the T200 and Sa3.9. The T200 was a great all around amp, even though only 100w/ch stereo. It was an "angry 100watts" however! Lot's of snap and bass weight. It was also very clear, detailed, and big sounding. I liked the amp very much. Would own one again if need be. Good stuff.
The 3.9 was, besides being less wattage (60/ch st), a bit sweeter on top, and midrange perhaps a pinch fuller from what I remember. It didn't however have the bass weight and smack of the T200 to be true. These differences however were small comparatively. Top to bottom, I liked em both just fine. Maybe the T200's trebble was a smidge "drier" sounding, but still excellent, smooth, airy, extended...as with both amps.
If I were driving a pair of modestly senstitive mini monitors, I'd lean towards the more sweat 3.9. If I was driving bigger speakers, or speakers with lower sensitivity, and I needed to rock a bit, I'd go T200.
I never heard the T400, which was like only 50 watts more power than the 200 or something. But I heard tell that the 200 was better, but not sure.
Anyway, that's my Treshold experience. All in all, good stuff indeed!

I agree with Exertfluffer's remarks on sound, but feel I should add that the T-series is not designed by Nelson Pass and uses ring emmitter transistors which are no longer available if they fail. Threshold service company can rebuild these amps with new output transistors and the existing power supply, but I have no idea as to the cost.

Jeff, you make it sound so easy; some of these vintage Threshold amps seldom appear online.

I've had a S300 Series II, and now have a S350/e. Both run trouble free and I keep mine powered 24/7. The stasis/e series are indeed the last ones with Nelson Pass onboard.

It's interesting to me that the S300 is a clean, simple looking design whereas the S350/e is much more complicated looking internally. Also, the S350/e came with not only an operating manual like the S300's but an additional separate service manual packed with schematics. Maybe it escaped me with the S300, but with the S350/e even the top cover has a part number stamped into it. The later over-attention to parts accounting makes me wonder what was happening at the factory shortly before it changed hands.

Echoing Oldears comments, The T series amps used IGBP's (insulated gate bipolar transistors) which are no longer available. Aside from today's Texas factory, a good repair resource for vintage Thresholds is:

http://www.rsvlonline.net/vintageamp/

Check out the archive there for some idea which Threshold is right for you. For my money, the optical bias later Stasis series (uprated A/AB from AB, have black top covers and say optical bias, instead of overall feedback free, on the front panels) and the e series are the cream of the crop. However I'm sure any of the earlier products reflect the same build quality. Real class acts like Threshold seldom disappoint.