It looks like you've solved the problem. I would also flip the Bryston's gain switch back and forth a few times, in case it's intermittent.
(I used a 14BSST for years -- a similar amp to yours -- and it is one of my favorite amps ever. Now I'm using a 4B3, which also is excellent.)
(I used a 14BSST for years -- a similar amp to yours -- and it is one of my favorite amps ever. Now I'm using a 4B3, which also is excellent.)