I think you are on the right track. Sound aside, ceiling speakers just look so sterile to me. Like a shopping mall or hospital or something. But that's just my personal feeling on their looks.
M2s on brackets would serve you well. With some thought on placement and a nice finish that matches the room, they should be fairly unobtrusive.
Cutting drywall is easier than you think if you decide to go with the W series. Even a rough cut is covered up by the border of whatever you are putting into the hole so it will look like a pro job when you are done, even if you don't have a steady hand.
Also wondering what kind of insulation you have. Fiberglass sheets usually don't pose too much problem for fishing as you can run the fish up along inside of the drywall without much trouble. (unless you have an old fish tape with a bunch of crazy bends in it) Other types of insulation can be tougher to impossible. 'Blown in' is a PitA.'
I know it's a living room but I didn't see mention of a TV. You mentioned you already have a high end HT system elsewhere. Just thinking that if it is just music, perhaps a stereo plus sub arrangement would be much simpler to work out. I really enjoy concert DVDs in 5.1 but with my CD/flac collection I am normally very happy in stereo as I tend to be moving around more during casual listening, so I'd rarely be in the sweet spots for surround listening.
