Here's the setup on my '94 850 wagon:
Kenwood Excelon KDC-X493 HU

Focal Access 2-way speakers with crossovers for the front doors and front tweeters

Focal Polyglass CVX coaxial for the rear doors

Stock rear pillar tweeters
Pioneer 700 watt mono AMP for sub
12" MTX Thunder sub in sealed box

Alpine MRP-F300 4-channel AMP for door speakers

Monster and Rockford Fosgate wiring all-around
The system sounds pretty nice at the moment. I plan on doing "The big 3" this summer and then possibly making my own sub boxes to fit behind the rear wheel well in the wagon. Possibly dual 12's.
all pics from Crutchfield.com