I had to give this thread a bump. Came across your post while poking around at work, and was amazed that someone else has the exact same problem I have. Same Setup, M60s and the vp100...receiver is an HK347 though. My complaint is the same...mp3s through computer via optical and cds via an Oppo 980 usually sound harsh. In my case, its generally the vocals that are noticeably off (I'm told the exact word is sibilant, but to me it makes singers sound like Sylvester from Looney tunes). I pretty much only listen to instrumental stuff now.
Did you get in touch with anyone at axiom? I'd be very interested to hear if the tweeter resistor option makes a difference.
I haven't gone the resistor route yet. What I've done so far is I've gone into each individual speaker "equalizer" setting and manually adjusted the higher frequency setting down to zero and adjusted some of the lower freqs up, pretty much made everything zero like suggested above. See the image of my FL speaker settings on a previous page. And backed the treble way off. Haven't had a chance to check all my music yet but what I have listened to sounds much better
Will post back here after I have a chance to listen to more different types of music. I know what you mean though, for the most part my recordings of female singers would drive me out of the room if I applied any volume at all.