I am using two Krell Evo 600E monblocks for R/L channels with music and home theater. The Evo 600e is a stunning amp. I use two Krell S275 amps for home theater only. One S275 amp is used to bi-amp my center channel speaker (my processor has 2 center channel outs) and the second S275 for the two surround channels. The S275 replaced my Krell 3X250 amp. I use cast for the 600E's, balanced connections for the S275's. The S275 is a much better amp than the 3X250 Krell. Since I don't use them for music, I don't have a feeling for their ability to create a 3 dimensional sound stage, dynamics, tight bass, transients, speed as I do with the Evo600e's. I have had no problems with the S275's, I like them very much. They are dead quiet and they provide more power than I need. They probably perform much better than the small Krell 150 monoblocks, which recieved very positive reviews. They are compact in all dimensions except for depth and weigh 50lbs each. The S275 is very nice, but it is not in the same class as the evo amps. If you plan to use the amps for music only and you don't want to pay the cash for a new Krell EVO e series amp, I advise looking for two Krell 450 mcx or 650 mcx monoblocks. I owned the 450 mcx's and loved them. They are great, extended frequency range amps (fast, detailed, 3 dimensional sound stage, great instrument seperation, nice highs, great tight detailed bass). They will not fit into a rack as well as the S275. You should be able to pick them up for a great price if you can find them. But keep in mind, you need a very good preamp and/or processor with the high end amps to get them to sound their best. I think the pre-amp/processor is every bit as important as the amp, if not more important. Hope this helps. Good luck.