Current and recent Bryston power amps have a trigger jack in the rear, which will switch the amp on and off when sent a suitable control signal (12V, but as I recall it's adjustable sensativity). Bryston preamps can send a suitable control signal, as can many others.
I don't think a Bryston power amp can control a subwoofer unless the sub has a signal sensing on/off circuit, but the same preamp which controls the power amp might also control the sub.
