Speakers for string Quartets

Agree with Sailboat & zgas.  I too spend much time listening to live performances of small ensemble string & piano.  Nothing will qet you closer to reality than Quads.  My 63s are highly modified but stock speakers will be magic if properly set up.  Match them with Spectral electronics if you can.  If you need dynamics & high volume look elswhere or get a second system.

Stradivarius.....jk... Big string quartet fan here, and I love my Harbeth P3 ESR XD's in my desktop setup. I bet their bigger brothers would sound terrific in your large room. I also love a ton of jazz and the Harbeth's really capture the intimacy and warmth of that genre as well. I had an opportunity to see the Borodin String Quartet perform the entire Shostakovich string quartet cycle over the course of 3 days, some years ago. It was truly a life-changing experience.

Why people use a subwoofer with magnepan i cannot understand. Put the money from the sub into your amp. Magnepan has the most natural instrumentale  bas not a pumping low instrumental low. And if you want the best musical low buy the dwm from magnepan.

Jazz piano genius Fred Hersch has a recent album with his trio and a string quartet...friggin' great stuff. I recently bought a Pass XA25 to see what that was all about and man, it's GREAT...giving my SEP Tube amp a rest. Freya, SA25, Klipsch Heresy IIIs  (I like the titanium midrange better than the new IV version) and 2 REL subs (the 2014th time I've mentioned this stuff)...strings for days along with anything else I throw at 'em, from Hindemith to Little Feat...who knew?

Besides Harbeth, you should definitely audition Spendor (but be sure it's the Classic line, you're more likely to find different lines that sound, well, different in stores), and Graham.  Unfortunately, neither Spendor Classic nor Graham are as easy to hear in the US as Harbeth.