So what you need is a pre-pro or AVR with preamp outs, and another with discrete analog ins. You preset the first pre-pro for your basic compressor input level, jumper all the other outs straight to the ins on the second AVR, except for the center which goes through the compressor. Go calibrate your compressor for center dialog. Then you can use the volume control on the second AVR to control system volume.
How's that for a kludge work-around?
Look, there's no easy way to do this. But have you tried any of the AVRs with a "Midnight" mode or something like Audyssey Dynamic Volume? Dynamic Volume increases compression on low level material, particularly the center. But you'll have to fool it after calibration, because it's going to set it's compression levels based on known in-room SPL. If you found an AVR or pre-pro with Dynamic Volume, after calibration you can raise the power amp gains and lower the pre-pro volume setting, thus fooling Dynamic Volume into thinking you're at a lower SPL than you really are. The result would be higher amounts of dynamic compression at higher specific SPLs. Might work, and save you the trouble a separate compressor, though you're into the world of separate power amps just to deal with the gain-fooling process.
Just an idea.
You can also solve your problem with a disc player that has 5.1 channels of analog out, though that's getting more rare and expensive, and doesn't address cable and satellite boxes.
I do feel your pain, though.