Well, I finished my open mod of my Pro700MKII. They look horrible now...I used a dremel and drilled out the outside of the headphone, and since the left side of the headphone has a PCB that allows removable cables, there is a piece of plastic hanging out. I'm not wearing these outside, so I really don't care what they look like. I filled in the holes with cotton, and that seemed to remove the OVERLY forward midrange. Plus there is less of a blare in the midrange--a byproduct of opening them up.
I can truthfully say that there is more detail in this headphone. Actually, these sound more like reference headphones. The pros were "musical" before, and now they sound more analytical. For example, the headphones now sound like a record player, and you hear the little static on it. The pros before had it, but it's more noticeable now that I've allowed the headphones to breath much more. Before, there was a sibilance in the 1K-4K frequency range (I don't know the actual frequency, but it's around there), and now the sibilance is gone. Plus, they sound a bit more balanced.
The bass of the headphones is noticeably increased, mainly because I've increased the amount of holes the drivers are able to breathe out of. It also sounds more accurate, there is more impact, and it seems to bleed in the frequencies noticeably less than before (when you're running ~36dB of bass boost, it will undoubtedly bleed). It also sounds a bit tighter and spacious.
The midrange is something that I have to get used to. Before the headphone enclosure was stuffed with cotton, there was a blare in the midrange, and it sounded like you just eq'ed the middle frequencies by like ~6dB. If you've tried it out before, then you know exactly what I mean. So, I lowered the values that corresponded to the blare I was hearing (my eq settings had the midrange higher than flat), stuffed in cotton, and that issue was fixed.
There is more extension in the treble. It still has the same tone (one notch away from neutral), and it is more pleasant to listen to than before.
The soundstage is much wider that it was before. It extends away from my ears more, and it projects in front and behind me better. This is the most noticeable improvement over the original pros. It is also easier to pick out where things are at because there is more space in the soundstage.
I've only listened to them for about an hour, but that's all it really takes for me to notice the sound differences between before and after. So far, I'm really liking the way they sound, and they've stopped me from buying the DT990/600...In the future I'll pick up a pair of the ATH-AD900 and swap out the drivers. They have the same driver size, the gel earpads should fit a bit better, and they are better constructed than these headphones. The wings on the top should also improve the comfort. It'll also look much better than what my headphones look like right now (HIDEOUS). I think that all of those factors make it worth $200.
I'm still toying with the eq, so it's going to take me some time to find the sweet spot for these headphones now.
EDIT: I'm blasting out my ears right now, and my ears aren't fatiguing anymore. Before I did this, the upper frequencies would really mess my ears up (I have tinnitus in my right ear), and whenever I hear a certain frequency (upper midrange), my ear would start sounding like there is a crackling sound. Now, everything sounds a bit more subdued and more pleasant, which is a huge plus for me. I'm listening to music on the loudest volume that I couldn't before, and there is no problem with my ear. Before, I couldn't listen to the songs at loud volumes because my tinnitus would prevent me from doing so. These headphones are so much more enjoyable now.
Edited by Trae - 12/17/12 at 6:38pm