About time you got here.... I pass you everyday on the street and was wondering how long it would take for you to find us.
The premium system is a bit annoying to work around. If you're dead set on not cutting up the harness you'll do well to use the link below for the stereo diagram. My recommendation would be to run new wire and not even touch the factory wiring. The stereo does have two antennas, one's built into the rear window (looks like part of the defroster); This is the one with the smaller plug. The regular size plug goes to the retractable mast antenna. Some people use an adapter on the smaller one and run both into a Y for what they clain is superior reception... some have had ghosting problems from this. If you drive only in the city and don't mind CD's or MP3's when away from the city then the window antenna is nice if you're looking to clean up the exterior and shave certain items. I generally stick with just using the mast antenna on my installs though.
Here's the wiring diagram:
http://www.cygnusx1.net/Supra/Librar...x?S=Main&P=132