Generally, the M2s are considered the right answer for the rears. The QS8s would work, but the M2s are recommended most often. The use of M2s apparently also gets you the EP500, so it looks like the right answer for you.
Having said that, there really isn't much out there that produces audio to take advantage of 7.1. Mostly it's 5.1.
To help the $$ discussion with the bride and get LFE which IS available all day/every day, you might consider skipping the M2s for now and go for the EP500 (makes for an easier discussion with the wife). This approach allows you to enhance the audio with a superb sub that will be in use al the time vs. spending money on rears that may not be used much. Might even get you to consider the EP600.
If 7.1 availability cranks up a bit, you could always order the M2s later (when the budget is a bit less stressed
).
