Best HT speaker system

B&W makes two classes of matched systems which includes the units that hang on the wall at the mid-point and/or rear. One is in the range of the 600/CDM series, the other is mulitple-thousands and in the class with the Nautilus speakers. They are both THX certified. See the web site which is BWSPEAKERS.COM

I guess there are four B&W classes in all Nautilus, CDM, 600, 300; All but the 300 series have a wall unit which would give you a 7 channel system if you used them at the mid-point and still had rears. If you really want the very best money no object the Nautilus line are excellent. The CDM-NTs are quite good also. I would consider using 7 speakers if you really want the best experience, and you may well see Dolby 7.1 decoders sooner than you think.

For HT I've become a fan of Aerial loudspeakers. They play loud and clean with good punch, and will provide excellent treble without getting harsh. You could run up front LR3/CC3B/LR3 (2x7", 1x5", 1x1" driver configuration), and for the sides and rears a combination of SR3s or LR3s. Not cheap at 1.5k each. If your budget allowed Aerial's new LR5/CC5/LR5 up front would easily pressurize your large room, but you may need more power.