Be careful, I tried a couple of the omnimount brackets that attach to the back of the speaker, and they wouldn't fit because the plate that attaches to the speaker was too tall to go between the port and the mouting posts on the back of the M3. Omnimount also makes some brackets that attach to the bottom, but overall I found that in person the omnimounts are large and rather ugly.
I also tried one of the smaller Vogel brackets and it was too small, didn't put enough distance between the wall and the speaker so you couldn't really angle the speaker down plus you might have an issue with the rear port. The larger Vogel mount with the bottom clamp would probably work, but you'll have to remove the grills from the M3 (not an option with my wife).
I went through an awful lot of searching and frustration trying to find mounts for the M3's. In the end, I found some black metal brackets at Lowe's hardware store that sell for $20 a pair and work pretty well. The only caveat is that they only use 2 screws to attach to the wall. If you're drilling into a stud that's fine, but I'm not sure if I would trust two drywall screws to hold an M3. Keep in mind when mounting a speaker that the weight is partly pulling
out on the screw, not just down like it would be when hanging a picture.
PartsExpress also had some brackets that look like they might work, I probably would have orderd the PANAVISE 110120B if I hadn't been desparate to find something locally ASAP.
Good Luck,
Jeff