I'm planning to purchase some M60s to use as main speakers. I mostly listen to music, but with 5.1 music formats coming (DVD-A and SACD), I thought I ought to consider adding speakers for surround. I can get hold of some NHT SuperOnes for basically no money. Would it be OK to use these as rear speakers in a 5.1 setup, or do the front and rear speakers need to be identical to get proper sound? Thanks for the advice.