When the red lights begin to flash - I've never seen mine do this - at what point do Bryston's shut down
I had the LEDs flashing red on a 3B (before the NRB/ST, with the flat front) some time ago. I had the Sonus Faber Minima FM2 connected to the amp. The Minima FM2, although being a small speaker with an 11cm (4 inch!!!) woofer and a Dynaudio silk dome tweeter, has a very low efficiency. The 3B was clipping although there was a MBL subwoofer between the pre and the 3B, taking off the real deep bass (<80Hz). If I remember correctly, I was trying how far I could go... The amp and speaker passed the test. The 3B never did shut down though!

I had a 9B ST shut down one channel once. But it was my fault, since there was not enough room above the amp, as it was a rather tight fit in the shelf back then (appr. 1/2 inch of room above the amp...).
Now my amps have grown (6B & 14B SST), have lots of room to dissipate heat and I currently live in a rented flat... so there is more headroom, better cooling and less opportunity to drive the equipment anywhere close to its limits... no flashing, no shut down.

Cheers!
Markus