I have the M80's in a room upstairs (12x12) that's setup for stereo listening.
I really like them. For a pair of bookshelf's they sound surprisingly good.
When I first got them, I took them apart. If I didn't like them, my plan was to send them back.
What I found was a heavy,(28 LBS each) well braced box. Also, a well made crossover, with metallized propylene capacitors, and shielded drivers.
When I purchased at $500, I thought that was a bargain. If you can get them at $320, they're a steal!