Here's my cabs....
I don't think they are for everybody; especially if you're into a more vintage, midrangey sort of tone.
We play pretty heavy hard rock/metal and they are awesome for that, but I still say that some things sound incredible thru them, some don't.
I ran an early Dual Recto thru one of them and loved it.
I had a Recording Recto pre that I ran with a VHT 2/90/2 and loved it.
But again, my tone is more scooped than your average Marshall guy, so it excels at that.
TONS of low end possible with these guys.
Right now my rig consists of my Egnater M4 -> Rocktron Xpression -> VHT 2/90/2 -> cabs.
These also sound awesome if you use a Crate Powerblock as a power section only with just about any preamp.
I have ran these six cabs in a wet/dry/wet setup using 2 cabs per section and it's insane how huge and awesome it sounds.
These aren't your grandpappy's guitar cabinets...
I've never tried other speakers in them, but would love to...though they fit my style so well, I've never been so motivated yet.