Given the size of your room, and the proposed set-up of your speakers, perhaps you should consider a slightly different Vandersteen option:
2ce Sig II speakers + a pair of 2wq subs.
Although your seating is a bit far back (given the distance between your speakers), your real challenge will be to load the room with bass. A pair of 2wq subs will do the trick. Plus, with the first-order roll-off 3 dB down at 120 hz, your main amps and speakers won't have to deal with sub-bass frequencies.
Personally, I think this would be a better option than either the Quatros or the 3a Sigs in your space. YMMV.
2ce Sig II speakers + a pair of 2wq subs.
Although your seating is a bit far back (given the distance between your speakers), your real challenge will be to load the room with bass. A pair of 2wq subs will do the trick. Plus, with the first-order roll-off 3 dB down at 120 hz, your main amps and speakers won't have to deal with sub-bass frequencies.
Personally, I think this would be a better option than either the Quatros or the 3a Sigs in your space. YMMV.