Sorry, but I don't know the specific details of Bryston power amps. In general terms, power amps with an in/out trigger can be daisy-chained so that when one goes on, they all go on. That being the case, I can't see how to stop the 9b turning on if it's daisy chained to the 7b, and the 7b controlled from either the Arcam or Bryston preamp without some logic to sense what the 7b is being turned on by. It should be possible to create a truth table to work out IF, THEN conditions then implement it in diode logic.
Thinking about it, if the 7b is turned on directly by the Arcam only, and the monoblocks are turned on by either the Arcam or Bryston, that should do it.
I've done a sketch, I'll scan it and append if I can.
Their are a few tracks I wouldn't mind having but I'm not paying the stupid money wanted for that box set.
No way is it worth anywhere near what they are trying to sell it for.
The profit margin must be massive.