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.