Does the radio head unit shut off?
Or do you mean the head unit stays on and all of the sound coming from the radio shuts off, uncluding normal speakers and subs?
Or, do you mean that the radio stays on, the sound stays on to the normal speakers and only the subs shut off?
If only the subs turn off, that sounds like the sub amplifier is getting either overloaded or overheated and activating the protection circuitry.
If the head unit stays on and all sound is shut off then the question is: how many amplifiers are you using? Do you have one amplifier powering all speakers? If so, it still sounds like the amp is activatiy protection circuit. If you are running the main speakers directly from the head unit and only using an amp to power the subs, then it sounds like the head unit amp can't handle the power draw from the main speakers.
If the entire head unit shuts off...well, that's something I've never seen before unless the protection circuitry is built in such a way as to power down the entire unit instead of dropping power to the internal amplifier.
2014 GT Premium [view my garage for pics and mod list]