Ok so my new question. Judging from those frequency charts, the ultrasone and the m50 have pretty much the same bass until mid bass and higher. Is it worth me spending 300 dollars or more to upgrade from my current pair? Is there enough difference in sound that I will immediately notice the difference between the two in terms of bass? I was thinking that maybe buying the digizoid and the q40 would satisfy my needs for 75-100 dollars less, I'm just scared that the q40 won't really be a great upgrade choice since that's also what I'm looking for, an upgrade...what do you guys think?
I haven't heard the Q40 in quite a while, so answering this specifically is a bit rough. But I really am not a fan of the M50 - they're boomy and congested sounding imho. And so uncomfortable. The PRO900 are a considerably better headphone overall (they aren't *just* a bass blaster - you can actually listen to music with them
). You'll have much better imaging, and comfort, and a very engaging and rich sound (as cel4145 mentioned). I wouldn't rely on an FR chart to be so predictive (it's only one piece of the puzzle after all).
wrt the Q40, I feel like you're probably right that they would be more of a "different, not better" kind of purchase.
As far as the HFI-2400 goes - I'd probably vote "pass" there; they're on the slower side, and somewhat dark; I think they do better with grunge and similar music, as opposed to electronica. This isn't to say they can't do electronica, but I'd rather have the 900s (or ideally, the 2900s (which have less bass than the 900, but are oh-so-much-more balanced sounding)). That having been said, for ~$180-$200 the HFI-2400 are a good value, and I'd gladly suggest them as an upgrade from the M50.
Regarding the Sony XB - I haven't heard the old ones, but I demo'd the new X10 (which I've read are either "cloned" from the XB800 or the XB900), and was not really impressed. They're not really offensive, but they're still somewhat congested, bass-driven, and have rolled-down highs (they aren't harsh or sibilant though, and that's a common complaint about the PRO900 - so maybe they're worth a look if you're sensitive to treble).
Overall my top pick would be the PRO2900, and then the PRO900, and then the HFI-2400 (and that probably lines up with pricing too
). The X10 should be available for demonstration at Best Buy (that's where I tried them), so you could get an idea of those without paying for them.
