Does anybody make...

Yes, adjustable gain would be correct.

I am building some Open Baffle speakers and I want to control each driver separately, I am just looking at options, My SSP-800 is in the shop again, ready to get kicked that into the closest. McIntosh C2700 offers one with 3 channels, which I believe the two outputs are adjustable... My OB are 3 drivers I was thinking 4 would give me some flexibility... I know a DSP would work, just looking at various options since I need a new preamp. 

thx,

Good luck with that one.

I think the Pass Labs XP-32 can do what you want. 
 

In its normal config each channel has two outputs. One has the ability to be adjusted via a smaller gain knob on the front of the chassis. 
 

You can order additional units to stack and control from the one main volume unit. 
 

Would be $$$$$ though.

Higher end surround sound processors with matrix routing would work.

Would an active x-over work?