Hello, I have M&K S-150 at the front and M&K MPS2525 at the rear (prof version of S250 tripole, same size as 150 but tripole) mated with a M&K 350 sub. I want to go 7.1 but short of £1700 for another pair of 150s what have other S-150 owners done for the perhaps 'less important' rear channel? I know this q has been asked in relation to the diapole v's monopole debate so rear seems to favour monopole, but not perhaps when used with such a good surround speaker already. Thoughts? Thanks!