Thats an old, very good idea, use a good full range driver for most of the spectrum and "add" a subwoofer and a super tweeter.
The Bazzilla speaker is kind of the same idea, I used to have a Lowther driver from around 100 hz to say 18k with 416 Altec woofers from 100 hz down and a super tweeter with just a Hovland cap (1 mfd I think) in series. I did everything to that setup, biamp, triamp, passive Xover Line level XO etc.
I would say, get a fullrange driver you really like and add an active subwoofer (velodyne?) and a supertweeter, forget about Active Xover the simpler the better, one amp for the full ranger and the supertweeter, connect the fullranger directly to the amp and a small Cap to the tweeter.
That way you are biamping with the sub´s amp and your fullrange amp. If you really want to go out of your way you can limit the bass response of the full range amp, either with a passive line level XO (PLLXO) or best way to do it would be to change the values of the coupling cap.
The full range driver (and cabinet) have to go lower than 60 hz for it to blend with the subwoofer...100 hz and you will need a Woofer (hence the Altec), not a subwoofer...
I am now using Cabasse speakers, I got tired of the Lowthers...