I have 2, 4u racks for running different systems depending on gig & venue size.
4u rack containing: - 1u Behringer compressor mdx1600, 1u vented blanking plate as my
2u Swr Sm400s bass head gets hot even though it has a built in fan & which i generally run in stereo mode,
which can power upto 4 cabs, but i ususally run just 2.
My second 4u rack contains:
Swr grand prix preamp, Sony srp l2000 compressor & a 2u Swr stereo 400 poweramp
which again i tend to run in stereo mode powering 4 cabs.
Superb & awesome sound.