Sanders Magtech, (stereo or mono).
Thanks, for the many suggestions. If it's helpful, perhaps I can share the rest of the equipment which is a bit of old and new.
Preamp: Marantz AV705
Amp: Marantz MM7055 (powers rear & side surrounds plus center)
Amp: two KAS2 (one is now broken, circuit board is fried so it probably can't be repaired)
Fronts, Apogee Diva Ribbons
Sides: Niles in ceiling
Rears: Heybrook HB.5
Sub: Velodyne ULD 15
Projector: JVC DLAX93D
plus the usual other stuff, bluray, svhs, turntable, power conditioner, etc...
So it sounds like I should look into Icepower and Sanders or perhaps a new Krell (which seem to be very pricy). My installer is recommending the McIntosh MC302 or a Mark Levinson N532H - but at about $6,000 that's more than I wanted to spend.
In the meantime, I had a Rotel RB-850 lying around that was unused so I hooked that up to the Apogee Divas. After rebalancing with Audyssey, it sounds 'ok' to me but to be honest, I'm not sure if I know what to listen for. I'm also a bit afraid to turn it up very loud but we just watched a movie at a normal volume and nothing melted or went up in flames :) Any thoughts on why just using the RB850 is a bad/good idea? Thanks again.
An amplifier with too little power or too little control at low impedance can clip. Watch your ribbons. Are they "dancing" when you use the Rotel? I am not familiar with Divas but the ribbons on my Apogee Stage speakers would dance with poor quality amplification but be rock steady with a good amp.
I use a McCormack DNA 500 amp with my Duetta Sig's, it's a powerhouse but he has other models that will work just as well. Try one of his models that will give you at least 200W into your speaker load and you should be just fine. If you want some tube bloom then try a nice tube pre feeding it.
Thanks to everyone for their advice. In the end, it came down to getting a great price on a new Classe CA-2300. I'm going to sell my working KAS2 unit to subsidize the purchase. Steve from krellservice is looking into whether the broken unit can be repaired. If so, I'll repair and sell that as well.