Two words - full range!
More words - or at least speakers that go down to the low 30s.
I have a very large room (39x19x9) and found happiness with a pair of used Alon V Mk IIs. I listen to about 70% classical and 30% everything else. I've always preferred full range speakers for classical, especially for the coherence required of large scale orchestral & vocal music.
My Alons play VERY loud if needed, without any strain or harshness, with a nice, extended treble, a rich midrange and solid bass. Very balanced. They are also quite open, dynamic and transparent, with a huge soundstage. They do demand a good quality, reasonably powerful amp, be it ss or tube. I drove mine with Herron M150 monos to excellent effect. A pair of Alon V MkII or IIIs will cost you $2k or under - which is a stone cold bargain. I think there's a pair for $1750 listed now. You won't get quite the same imaging characteristics with floorstanders as you do with monitors but the Alons image very, very well.
You might also look for the the full range Alon Lotus Signature Elites with the 16 ohm woofers - they were specially made to be sympatico with tube amps and possess more than enough cojones for a room your size.. 50 tubed watts is more than enough to drive them. Alas, they are no longer in production although the pop up here from time to time.
I've heard the Zu Druids on classical and they did not do it for me. They are fun and they boogie but I wouldn't want to own them, especially if I were primarily playing classical, opera and vocals. Just my 5 cents YMMV.
