I used to biamp in the early 90's. I used an Alembic F-1X preamp into a QSC USA 1300 power amp, and I ran a Peavey 2-15" BW cabinet for my lows, and a 4-12" Peavey cabinet for my highs. I dug the power of the QSC and the F-1X's tone, but I had a hard time balancing the high/low setup during gigs, but YMMV.
I can't recommend the Crest CA9 power amp enough to folks wanting to run a rackmount setup. But be forewarned, it weighs close to 50 pounds by itself. But I've never felt a lack of volume or headroom using it. It's truly a monster of an amp for bass guitar.
I'd say the combined weight of my rack with the CA9 and my Demeter HBP-1 preamp was close to 75+ pounds. I'm by no means slight in build, and I've been doing physical labor for the majority of my life. I'm 56 years old, and I can still move my rack without much difficulty, but I also rely on a convertible hand truck/dolly.
Before I play another gig, I plan on putting the CA9 in a rack by itself.
I'm now using a GED-2112 preamp, and with a stereo power amp, it allows me to run it's separate Deep and Overdriven channels simultaneously into separate speaker cabinets. For the heavier styles I'm now playing, I've never had a better amp setup.