Now then. Get a coffee.
I ran a tri-amp set up in the 1990's; I was running so many cabinet combinations it was mental. I had a rack with a Trace GP12SMX preamp, a Trace PPA600 stereo power amp and a mono powerstage (which could have been a Trace, but I don't remember). I could feed this into a combination of an SWR Workingman15, a Goliath 4x10 and a Trace 4x5 bright box. There were other cabinets. It did sound huge, but it was ridiculous really, especially when you rock up to a gig and your guitarist is sporting some little combo, so It all went. Speaker technology has come on somewhat since then.
Interestingly, the crossover thing. I used a Rolls SX21 for a while in an effort to get a decent tone out of a Waterstone Tom Petersson 12-string. It did work really well and I was able to route the fundamentals through one signal chain and the octaves through a second dirty route; there was very little spillage and it was a sound investment at the time, so it's highly recommended from me. I wish I'd hung onto it when I moved the Petersson on.