I can't speak for Axiom or the Focal Chorus line, but I've auditioned the JM Lab Grande Utopia (about $120,000 Cdn) and it's inverted beryllium tweeter, and haven't found anything about it that would make it more or less effective than a standard dome tweeter on other megabuck speakers I've auditioned.
If you're already happy with the 806's, I'd consider an active subwoofer first. It might take a few weeks to tweak the sub placement, volume, and x-over, but you'll usually find that even full range speakers are enhanced with a good sub.
If it means anything, there are NRC measurements of the Chorus 706 on Soundstage.com, and it, and the various Axioms, are sonically more neutral than a $24000 Wilson Audio WATT/Puppy 7 speaker or $10,000 Krell Lat-2 speaker system. Sucks that more money doesn't mean better sound, huh?
