I have had Quads in my system but never owned them. Gorgeous mids, as you'd expect, hated their LF and the top end never quite sounded "right" to me. Back them Decca ribbons were a common addition. I heard an HQD system that was pretty amazing, way back in the early 80's... Nothing like a pair or quad of 24" subs driven by a few kW to shake things up. Back to reality, and Quads, I used a passive second-order (LC) line filter to roll off the bass to the Quads. Without that, I was overloading them too often on strong bass, things like the old Sheffield Drum record and such.
I built my own, and at the time also had an ARC crossover that did a decent job (but was dedicated to other uses). Marchand makes passive crossovers too, though even those are not cheap (~$1k IIRC). I first tried a simple first-order filter but when I put the crossover where I liked it the roll-off was too slow. It's all preference, though.
I have been thinking about trying Roger Sander's speakers -- their place is not too far from me and they've invited me up, just never found time to get there. Partly because I can't afford to walk out with new speakers, much as I'd like them... I've always liked ESLs but never actually owned a pair (though heard many through the years). Maggies offer a different set of trades and I have been happy with them, especially since they added the ribbon tweeter.
I set up several IRS systems, and had IRS-II's for a time, but back them the reliability of EMITs and EMIMs was less than desired, and I fell in love with the Maggie sound despite the bass and dynamic range drawbacks compared to the IRS. Plus they took up a little less floor space, and were orders of magnitude easier onthe wallet!
Small world - Don
p.s. To add some relevance to this thread, back then I decided servo subs were the only things that would integrate well with panels, ESLs or Maggies, without spending a major fortune on subs and amps. I rolled my own, but am very happy to have found Brian and Rythmik for my current system. Compared to the other subs I auditioned, amazing performance and value, not too mention a very dedicated designer.