Thanks for the response ! I'll look into the Blaupunkt H/U's, especially if the Sony doesn't work out for some reason.

Somewhere in the thousands of posts in this forum I came across a wiring diagram for the stereo system, which seems to show that the stock amp has four channels, though several XF models (all 2004 coupes and 2005+ non-Base models) have 6 speakers... The door and rear speakers seem to be wired off the same amp channel. More to learn....