Threshold "T" vs. "S" - whats the differences

can anyone shed light on the differences between the two Threshold models - the "T" series and the "S" series.

thanks for any feedback or recommendations
I believe the S and SA series were made when Threshold was owned by Nelson Pass. When it changed hands the amps appearance and numbering (as well as circuits) changed. IMHO the SA series, non optical bias, were the best amps ever made by either Threshold company.
I owned the s/300 series 2( non optical bias ) and it was manufactured around 1990-1991 if my memory serves me correctly. I also believe that the "S" series was the best Threshold ever made.The T series is a later version and in my opinion once they changed from the "S" series Threshold was never the same.
T is IGBT's and S/SA series is tranny based.

The S and SA series were designed by Nelson Pass when he was a co-owner of Threshold. The SA3.9e and SA-4e series in particular were great sounding class A amps.
The T-series were designed after Nelson left Threshold. They were also good sounding amps, but have the disadvantage to have been designed around the IGBT output semiconductors which are no longer availble if there are problems. I understand Threshold still exists as a service company and will completely rebuild the T series with new semiconductors.
Didn't the S stand for Statis? Also, the A series (their oldest) were pass designs. The 400A and 800A were great
Take a look at a following link:

Nice info about Threshold stuff from the first amp to the "T" series (with pics).