Which speaker will perform

With all due respect, you can run either! I may be missing the gist of yr question -- unless you're asking which of the two spkrs to chose?
If so, is there no way you can listen to the ML-2's driving either pair and chose by audition? Cheers

Those ML's are great amps with tons of current but I doubt that you will find them powerful enuf to drive those Kappa 9's. Even high current 200wt amps have problems. There was a recent post on this Speaker - you might see if you can find it. It included a lot of recommendations - but, I think you will find the consensus would lead to to not purchase the Kappa's - they are just too hard to drive. And, if you wanted to "voice" your speakers by amp selection you would have very few choices. Can't comment about the 804's, but I've heard the ML2's driving Quad 63's and was very, very, impressed.