Jdh9:
I have Threshold amplification also and love it. I used an S/500 for a couple of months before buying a pair of SA-1. In the interrim, I also had a chance to listen to the S/200. I found the S/200 to be a little sweeter than the S/500 but without the authority of the bigger amp. I have Apogee Stages: relatively ineffiecient at 87 dB/W. The extra power of the S/550e may not be of any help to you with your B&Ws.
I can't comment on the "e" modifications since all of my Thresholds have been earlier amps than those.
I have Threshold amplification also and love it. I used an S/500 for a couple of months before buying a pair of SA-1. In the interrim, I also had a chance to listen to the S/200. I found the S/200 to be a little sweeter than the S/500 but without the authority of the bigger amp. I have Apogee Stages: relatively ineffiecient at 87 dB/W. The extra power of the S/550e may not be of any help to you with your B&Ws.
I can't comment on the "e" modifications since all of my Thresholds have been earlier amps than those.