I keep a vintage pair of MG-IIIs, which are the much older brother of the 20.7, approximately the same size, approximately the same frequency response, approximately the same impedance
Year: 1987
3-Way Combination
TR tweeter : ¼″×57″
midrange : 170in²
woofer : 620in²
Frequency Response: 32Hz-40kHz ±3dB
Crossover: EXT: Low-Pass 18dB/octave @ 300Hz
High-Pass 12dB/octave @ 500Hz
INT: 3kHz
75-200Wrms @8Ω
85dB/2.83v/m @500Hz
4Ω
24″ × 71″
130.lbs
Your Bryston amps are ideal high-power amps, which will deliver 500 watts to the 20.7 4Ω load.
Yes, they need space. Presently mine are in a 16' x 27' x 9.5' foot room, which is just adequate for them to shine. A bit wider on the short dimension would be better. These speakers want space and can deliver a very wide, but detailed soundstage. They are incredibly transparent - they truly disappear behind the music they deliver. Their single weakness, if that is what it is, is their frequency response - which seems to have been addressed in the 20.7. I see no downside in that option if you have the room for them. One bit of advice: Throw out the "Speakers must go this way" book, and experiment with placement, Bipolar speakers lend themselves to different options depending on their surroundings. Just try multiple options, you may be pleasantly surprised.
http://www.integracoustics.com/MUG/MUG/articles/speakers.html
Enjoy!
Peter Wieck
Melrose Park, PA