Hi all, long-time reader, first post. I'm using an Auzen Prelude with HD650 connected direct to the line out (LAME or FLAC files, bit-matched playback, ASIO, fb2k). I'm sure pretty much everyone around here thinks I need a headphone amp to get the best out of them. I don't have money to burn and so am considering a Matrix M-Stage, which seems to get good reviews and is relatively inexpensive. I'm not looking for amp recommendations - my question is: why do I need one at all? I have a very discerning ear, and my HD650 don't sound 'veiled' at all. On the whole, they sound bright and detailed. They do *occasionally* (i.e. with certain recordings) sound slightly unrefined to my ear at the top end, and a little muddy in the lows, but that's being very picky, and it could just be clipping in the recordings themselves. They also go so loud that I never turn the volume above 50-60%. I see that on paper, the M-Stage op-amps aren't as good as the front L/R op-amps in the Prelude. I know amplification isn't all about op-amps, but what is it that my Prelude isn't doing that a decent head amp will do? If somebody has an answer that doesn't involve subjective claims about sound quality that would be very much appreciated. I'm not convinced an amp will make any difference at all beyond placebo, and am looking for an objective explanation of *why* such headphones sound so much better with an amp. Thanks in advance.