As for whether it's you or the room that accounts for the brightness you hear, either is possible. I will mention that, over the Christmas holidays, in that audition with the C2300 and the MC275, I heard a C50 (same audio circuit as the C48) paired with an MC303 (I think) driving Revel speakers. That sounded really nice, not bright, not to me. But the room did have some treatments, and Revels are very nice, a bit to the warm side like my Mirages.
Perhaps you could try different speaker cable or interconnect to see if the sound changes with the C48/MC601 setup. Throw a CD in there also.
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