Scott, welcome. Your plan looks good. The M22s with dual mid-woofers will have a capacity to play a bit louder in the mid-range and upper bass(above the STF-2 coverage), but this may not be a significant advantage at your listening distance of 7' or so and keeping at safe levels. The M2(or M22)should also be selected for the center speaker under the screen.

The 508 should be an excellent choice. Note that the Accessories4less price is $179 plus shipping(if that isn't what you were quoting).

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Enjoy the music, not the equipment.