A few systems have RS232 inputs so to meet your requirement of not using the remote we would have to check out what other control inputs this system has. Once we find out more then we can look into some small computer board with RS232 to send the command when something happens.
This will get technical and cost a few hundred so the owner has to decide if it's worth the work and cost.
I'm still not sure if this is the right place to ask.
I've an old 5.1 home theatre system with IR receiver on the front of the subwoofer. It can be turned on only by pressing the power button on the remote control. Otherwise it'll stay on standby mode after turning on the electrical power switch. That is if any power failure occurs (even for a few seconds) I've to press the remote button everytime. The TV and STB turns on by itself but this thing doesn't. Is there any way to turn the speaker system on without the remote?