There is a couple threads on this already
Do you use a USB drive for music?
Mine would shut off at higher volume, I replaced my USB and installed an OEM audio subwoofer, checked all connections on the back of the headunit
Haven't had it shut off since
Here is a thread on removing the headunit
http://www.ft86club.com/forums/showthread.php?t=30144
Here is a video
[ame="https://www.youtube.com/watch?v=kAWRRJcxWkI"]Subaru BRZ Stereo Removal - YouTube[/ame]