Using Professional Amps On Home Theater Speakers

.
The Kappa 9 will bring the Sunfire 5 x 400 to its knees....it won't wake up the Kappa 9, they just don't have the muscle at 4 ohms and below to get the job done. I've owned the Sunfire Signature stereo amp at 600 wpc and they performed only satisfactorily with the Kappa 9, I needed two of the Sunfire Signature amps in a biamp configuration for superior results.
.

70 ft long room. Is that a business,or institution or home? What are walls made of and covered with? Flooring?

.
Doc, it's a loft that I live and work out of. It used to be
an industrial building before the conversion. Very thick
carpet and padding over a concrete floor..... and ceiling is
concrete also. Walls are drywall with insulation with
neighbors on both sides.
.

I've not listened to the Kappas and certainly don't know the real power or current they require to perform properly.

Also, I do understand you are just looking for HT sound, not top quality two channel performance.

Normally, I would not recommend a digital amp as I don't think they are very good with traditional driver speakers with regards to two-channel performance (I have never heard a Class D amp I was impressed with for this type of speaker and I have heard many and owned several). For the record, I think Class D amps are best on ribbon and planar speakers - but that's it.

But in your case, and since you don't seem to care that much about the quality, perhaps you need to lean in this direction. Though I have to warn you that my Bel Canto Ref. 1000s (1000 watts at 4 ohms per channel) were not powerful enough to properly drive my Thiel CS 6s while at the same time, my Mark Levinson 334 at 250 watts at 4 ohms did not have any problems in my sized room driving the same speakers.

What amps do other users of these speakers use to drive them? Are these speakers really designed to address that volume of space?

I know when my son DJs and he needs to cover a larger space/volume, he ends up having to use many subs (sometimes 6-8 total dual driver or sometimes quad driver sub/low bass units and is running thousands of watts just on the subs) just to properly pressurize the large room.

Why not go to Guitar Center and talk to the guys. You can rent a DJ rig for a weekend (excluding the speakers) or at least the necessary amps. Guitar Center lets their employees rent stuff privately, so you can probably get away for a few hundred dollars if you are just talking about the amps and the cables. It will give you an idea of what the sound will be like.