I own the RX6 (upgraded from B&W 685) and couldn't be happier. You definitely get more speaker for your buck with the RX6. The CM5 are nice speakers, and will probably eke out a bit more detail when compared to RX6, which I found a bit more laid back when comparing the the CM8/9 range. FWIW I preferred the MA sound, and think the RX6 are a much better value compared to the CM5. If you're looking at the RX lineup, I find their centers are much better than the 6-series B&W centers, too.
ht Panasonic TC-P60ZT60, Monitor Audio: Silver RX6, RX Centre, Radius 90HD; Martinlogan Dynamo 700, Marantz SR5006, PS3, Oppo BDP-103D
2ch Marantz PM8004, Sony BDP-S1000ES, JVC T-X3 tuner, Monitor Audio Silver RX1, REL T3, Apple TV, Peachtree Audio DAC•iT
lr Panasonic 50ST60, Sony BDP-S5100