Well, I'd be connecting those speakers to the MC75s first for a quick listen. Sure, they've got a rep for being difficult loads, but MI75s (industrial version) were used for all kinds of difficult loads in industry, etc.
Don't be afraid to play with the connectivity of the speakers to the amplifier speaker taps in an effort to get good sound. Once you've determined which taps drive the speakers best, you may find that you're all set. On the other hand, if you can't get the Kappas loud enough, you may elect to move up in power.
I'm the wrong guy to ask "how big of an amp do I need?" . . .