Just different amps. Monolith 5 is a 200wpc (8 ohm full range) and 300wpc (4 ohm full range) for $1300; the Outlaw 5000 120wpc (8 ohm full range) and 180wpc (4 ohm full range) for $650. Whether the Outlaw is a better deal somewhat depends what wpc you want. I'd use either amp happily, they've both tested quite well and seem to have quite a few happy users. I'd just get the Monolith 7 for $200 more, better value in that sense.
You could do something like three Crown XLS 1502s for 6 channels of amplification (300wpc 8 ohm, 525wpc 4 ohm, 775wpc 2ohm, different basis
but borne out in bench testing at least into 8 ohm, where it did 336wpc in 8 ohm) for $1200 or so. It's a pro style amp but would work well. I've had several of these (altho the previous model, the 1500) for years and am quite happy with them.
Those two models from D&M are fairly similar, I'd get whichever I got the better deal on.