For information on how to remove the OEM HU, dash, panels etc ....
Visit
http://techinfo.subaru.com/search/index.html and search under Accessory Installation Guide as publication type - (Its free)
There are 3 guides (Aux Input Jack, Power Amp, and Power Outlet)
that have pretty good instructions. You'll find where all the panel clips/screws are located.
Didn't know you can post a direct link as iLoki did above. Here they are:
http://techinfo.subaru.com/proxy/661...xInputJack.pdf
http://techinfo.subaru.com/proxy/663...H630SFJ000.pdf
http://techinfo.subaru.com/proxy/661...owerOutlet.pdf