I'm not going to wade into the series/parallel discussion on the Quads. But I would like to come back to the Golden-Ear's question, which is a fair one. I am making the assumption only because I know the characteristic sound of the Quads, which is a bit 'polite.' Yet, I've heard the same thing I am describing on a big system that I had a fair amount of seat time in front of, using Dunleavys and Krells with what was then a first rate front end. So, it ain't just the speakers, I agree. But, the thing that does intrigue me about the horn approach is the ability to render big dynamics, and create that 'alive' feeling that you get in live performances.
My front end currently consists of the Lyra Parnassus, running into an ARC SP-10. (I am currently using a Sugden phono stage, but the same constraint existed with other, higher output MC cartridges run directly through the SP-10 phono section- The Well Tempered Classic, somewhat tweaked, is the front end). I don't know if these components impose a straight jacket on the music- I was actually thinking about upgrading preamp next, rather than TT (I'd keep the Sp-10 for funk value). The amp, as noted, is currently an ARC Classic 60, which provides ample power for the Quads, and has loads of 'image depth' if not a 'whitish' upper range. I have not tried a digital front end, and doubt I will....
THanks again, for all the good input. MOre updates soon on the progress of my Quest...