Ok, I've gone to Swedespeed, Brickboard, Matthews Volvo Site and Brickspeed to find the answer to this question, but I'll come back to the most active Volvo forum I know, Tbricks.
Still have my RWD cred, as I still own a 91 945SE, and a 72 1800e. But I needed to move to a Volvo from this century for my daily driver.
I've just bought a 2004 Volvo s80 AWD, with 5 cyl. Turbo. It has the basic audio system with the HU-611, with cheap speakers that are paper cone woofers and paper cone tweeters. I've been able to find a 2000 Volvo S80 that had the better woven speakers, HU-801 and the amplifier (4x50 watts) under the passenger seat.
I've learned that you can't swap the headunit, unless the cars are the same model year, but need to know if I can I attach the underseat amplifier from the HU-801 system to the the HU-611 system?
Hopefully one of you out there has tried and can comment.
Many thanks,
Bruce