Purpose of using same speakers for surround?

Some room correction software will give you a visual of the performance of your individual speakers and their locations. Some programs will match to the weakest speaker. Given some work in their placement a matched set will need much less correction if any.

It's difficult to appreciate the potential of your system until you can compare it to being properly setup. As digital film production improves and with Blueray audio looms on the horizon the quality of your multi channel will become more important.

I just saw Mission Improbable at an Imax theater. While I couldn't tell exactly what speakers they were using for the rears they were very large PA looking. I don't go in much for today's shoot-em-ups but the previous MI's were at least somewhat believable, well subjectively anyway.

The sound track had some moments were the rears were at a very high volume with almost nothing coming from the front. Seldom used, the effect was very dynamic. Numbed by the shear excessive use of what's become one note explosion low frequency the audience was clearly startled by this massive discrete jolt from the rears.

Is this an indication that film audio is beginning to get over the ridiculous? Maybe not.

In my previous 5.1 system using "surround" speakers the effect was novel compared to my current 7.1 using matched speakers. As a reminder, 7.1 is not about room size. It works very well in a small room.

If your combining two channel and HT you need to bias the quality of one or the other. IMO two channel is simply too delicate. That said, matched speakers are worth it.

Baxter, is there a small version of your M7's with similar drivers? I think if you pole people using matching speakers they're usually small bookshelf sized speakers with a subwoofer.

Matching floor standing speakers might be overkill and difficult to locate within your room compared to wall mountable speakers.

Titles using 7.1 is small but growing. Most modern 7.1 receivers have the ability to matrix 5.1 into 7.1 with very good results creating a more discrete surround effect in most any size room. You won't find many 7.1 users going back to 5.1