Edited by Craigster75 - 5/31/13 at 2:23am
The bass on the PRO 900 is quite commanding - it is strong, tight and has a lot of mid-bass. On bass alone, the PRO 900 is better than the M-100. Hell, it is definitely one of the best basshead cans around.
However, as an overall package, unless the treble is attenuated, I very much prefer the M-100's comparatively darker sound. Like many others have mentioned, the PRO 900 is quite harsh, and bordering on sibilant. This depends on your preferences - if you like loads of treble presence, and strong bass, the PRO 900 is definitely a can you should consider.
Auditioned the D600 yesterday... WOW. The bass was just amazing, and everything else seemed well balanced too. Mids weren't recessed, highs had a decent sparkle but not piercing or overdone at all. Haven't heard the Pro900 so I can't compare.
I don't remember my Q40's bass sounding this good. Power, authority, clarity, and each bass note was clear as day. Maybe it was partially because they had a huge (probably high end) amp the size of a home theatre receiver. In any case, at the retail price they're way more expensive than anything I have, and more than I can afford. But boy do I want one
I gave the HD700 a whirl too, just to see what "high end" sounds like (they didn't have an HD800 on display). Clarity was unholy but the treble made vocals sound a bit artificial to my ears. HD598 had a similar sound.
I wouldn't keep more than one pair of headphones that sound similar. What's the point? Just keep the one you like best, and sell the rest. If you're going to have multiple pairs, they should at least be different
By the way, $240 for a pair of used D600 would be a pretty similar price to a pair of used M100. I know you haven't had the M100s for very long, but which do you think is better? I think the Craigster likes the M100 better, if I'm not mistaken.
Similar doesn't mean anything. Similar still implies SOME difference. Difference both large and small are both equally important to me. I own both the Sig Pro and the Sig DJ. I am probably the only person that does. And I use them for totally different music one from the other. NOT that the other still doesn't excel at the other's genre, but there are small tweaks that make one can much more preferable for different genres.