Another option is to hide the cd-changer and swap the speaker lines from the changer to the empeg leaving all other wires to the changer. This would maintain the ability of the headunit to accept auxillary input (this is required for GM's, not sure about Suburus) The only thing you may need is an inexpensive linelevel adaptor. If interested see:
http://empeg.comms.net/php/showthreaded.php?Cat=&Board=install&Number=119128&page=2&view=collapsed&sb=5&o=0