try and triger it from the cars ignition.
i was lazy when i did mine and went with the decks amp trigger..
the deck usaly delays the amp for a second or 2 to prevent that anoying poping noise. and then the opus takes a few seconds to switch on aftr being triggerd..
in other words witht he opus hooked to the amp out it can take about 5 secs to switch on and theres a fair chance of that pop..
hooked up to the ACC and it will take less time to switch on and theres less chance of any pop
I've got it hooked up to the acc at the moment, but I don't want the pc to come on whenever I switch the car on. I want it to come on when I want it on... If that makes sense. I had a switch between the ignition and opus in my previous car but that was a bit lo-tec.
Another reason I use the headunit to signal power on, my car has a feature where the stereo stays on after you shut the car off until you a: open the door or b: 5 minutes pass, then it shuts off. It's a great feature for listening to the end of a song or radio segment without running the motor. By tying this to the HU, the computer stays on by the same rules.