I've tried this.. let me explain a little further. The cable I used to connect to the backside is a straight-through one and this works. The cable I modified is a male-to-male one and I've tried uncrossing and crossing the lines. Weird thing is when I do not uncross the lines for this modified cable I hear a slight pulse through the speakers, once per second which goes away if I turn off the GPS unit.
Which makes me think the GPS is definetly working since that sound is the NMEA pulse, but something weird is going on preventing the signal from getting to the empeg.