Trigger activated softstart/turnon kit available?

Hi All

I'm doing another holton precision audio build, probably dual mono NXV500 but I also want to incorporate a third center channel amp inside the same case with it's own power supply/toroid and a trigger controller so that the third channel is only turned on when I turn on the AVR to watch movies/tv etc. At all other times the power amp L and R will have a mom push button switch at the front wired to Anthony's own mains controller - which only has 1 "switchable" output.