Speakers for 7.1 vs 7.2 - Mix and Match

I am completely upgrading an a/v system, and am purchasing the following:

Polk Monitor 70's for (2) Front Speakers
Polk Monitor 30's for (2) Side Speakers - mounted at edge of ceiling/wall pointing downward
Polk Monitor 30's for (2) Rear Speakers - mounted at corner of ceiling/wall pointing downward
Polk CS2 center speaker, under my 63" Rear Projection TV, leaning upward

I am debating the Polk DSW MicroPro 1000 for the subwoofer behind the TV.

I am hooking to an Onkyo TX-NR807, which has 7.2 capability, and trying to decide whether the 2nd subwoofer is needed, and whether to go with (2) Polk PSW10's instead, with one behind TV and other behind couch.

Room is wood paneled, 15 x 22, with TV and AV cabinet on 15 ft wall.

Also, am I better off to run speaker cable under carpet or in wall? With paneling, its a bit more tricky to put new boxes in.

Thanks for any advice!

also, any ideas on locating brown cabling to run to the speakers? The clear copper wire definitely shows up when running up the corners of the paneled walls. Is 12g 2 wire electrical cable ok to use?