The problem with the Mac amp (in my 08 gtb anyway) is that its input connection is a special multi pin round screwed on unit. I replaced my HU with a jvc dvd capable unit, tossed the amp altogether. This leaves you with a speaker connector under the pax seat. I got a cable and connector from svxdc (
http://ae64.com/), soldered the leads to the jvc output leads, and away we went. Had to remove the pax seat to do this properly. If you use the factory JDM facia from AVO japan, it comes with an adapter cable from Suby to a std coax aerial plug the fits most HU - make sure you get the correct version, for either single zone AC or dual zone. There is a thread of mine from years ago where I did this originally on an 04 Outback, then moved the whole lot to my current car around 2008.
jp 08 gtb 6mt wagon