Okay, stoney, if the budget can handle something in the area of $3,000 I'll make a few comments. I'd generally agree with Mike's suggestions. The reason for a vertically oriented center speaker is that, contrary to your supposition, it generally(I'm not familiar with the VP150)has a wider and smoother horizontal dispersion than a horizontally configured center. Setting an M60 horizontally would lose this advantage, and with an RPTV you apparently wouldn't have room for a vertical M60 center. You could consider whether you'd have room for a vertical M22.
As to the placement of surround speakers in a 7.1 setup, the side surrounds should be directly to the side(not behind, as would be better for 5.1)and 2-3' above ear level. The back surrounds should be at the same height and separated about as far as they're behind the listening position(e.g. if they're 6' back they should be separated about 6'). Note that although there's no discrete 7.1 material presently, your 2500 can use DPLIIx to extract ambience from the front channels in two-channel materials and the side channels in 5.1 material and send it to the side and/or back surrounds where it belongs.
