THETA DREADNAUGHT II TRIGGER

Pull the trigger wire and see if that causes it to turn off.  If not, it is probably a bad relay.  An inexpensive fix.

Before I had a Krell TAS amp and works fine also on the Mcintosh manual says the trigger 1/8 plug has to be stereo and on Theta says 1/8 mono plugs

Some older Classe and Proceed amplifiers and the Theta Dreadnaught II need pulse signal to activate its remote trigger. You need a adapter to convert your preamp 12V constant triggering signal to pulse signal.

http://Theta Digital Dreadnaught II Owner's Manual

Remote Triggers
When the rear panel STANDBY TRIGGER jack receives a 5-12 VDC pulse, the Dreadnaught II will change its state from either standby to operate, or operate to standby, depending on what the current state is.
When the rear panel SURROUND TRIGGER jack receives a 5-12 VDC pulse, the Dreadnaught II’s surround buss will change from its current status, either on or off.
Use a 1/8” (3.5mm) mono plug for these jacks.

An stereo to mono adapter or a stereo to mono 1/8 cable?