Tom, the 2003 and the 2004 are different. Don't quote me but I believe the UQ7 is the premium bose set up. The amp is the difference. You are gonna lose the fade control on any aftermarket head unit replacement unless you replace the amp. I can save you some research. Contact Robert Wilson VP of Sales, Pacific Accessory Corp.
www.pac-audio.com or Joe Hobart of Soundgate
www.soundgate.com These are the companies that make the bus interface adapters, if these guys don't know....I doubt anyone does. I tried bose...no help. I tried hummer....no help. I even contacted helminc for the wiring diagrams for the speaker and amp set up. I was told none is available as of yet.
Hope this helps.
Garry