Yesterday I have finally had a long session with Fostex TH-900MK2. Until now I only took it out of the box couple of times since the purchase, despite being back home for 2 weeks already.
I completely forgot about burn-in, so could only compare ootb TH-900MK2 with burned-in Pro 82.
Update: the impressions below were updated to reflect the burned-in TH-900Mk2
Comfort:
The default TH-900MK2 pads are quite uncomfortable when installed with the thick side in the back (default).
They also have almost zero isolation - now I understand why
@Ossy_TK was asking if they are semi-open.
Rotating the pads 180 degrees helps to improve comfort and isolation, but not as much as installing TH-610 pads.
With the TH610 pads installed, Pro 82 and TH-900MK2 are very close in comfort, still with a small edge to Pro 82
Isolation:
Isolation is much better on Pro82. In a quiet office, when no music is playing, I can hear AC working on the Fostex (even with TH610 pads), but not on Takstar.
SQ:
As far as sound goes, TH-900MK2 isn't nearly as impressive ootb as it was in the store. Burning seemed to help.
Bass - Bassheads will more likely prefer boomier bass on TH-900MK2, it has better decay.
Audiophiles may go for the tighter bass on Pro 82.
Both go equally deep, but TH-900MK2 has a couple extra DBs in the bass.
Mids - TH-900MK2's mids are more forward, but slightly less clear. While vocals sound fuller on TH-900Mk2, I do prefer the amazing clarity on Pro 82.
However, you can tune Pro 82's mids to sound more like TH-900MK2:
Tuning Pro 82 with easy mods
You can't tune TH-900MK2 to have more clarity...
I'll still take B8 over both TH-900MK2 and Pro 82 for vocal-heavy tracks.
Treble - Equally extended and clear on both, but Pro 82 sounds a bit more energetic and detailed - maybe due to more recessed mids.
Soundstage:
Th-900MK2 has a larger soundstage, yet often somehow sounds more "headphone-y" - like it's trying to fake it.
The amazing clarity of Pro 82 combined with more intimate (but not small!) soundstage results in better experience of presence.
Conclusion:
So far, TH-900MK2 and Pro 82 sound very close, much closer than Pro 82 and Pro 80.
I did think a few times that I had Pro 82 on my head, while it was actually the Fostex.
Afterthought:
When I was shopping for new headphones, I left Pro 82 in the hotel, and was only comparing the Fostex with other $1000+ headphones, most of which were very disappointing.
So it's possible I would have walked out empty-handed if I had Pro 82 with me...
The comparison above was with Pro 82 v1, the newer v2 version sounds even better, removing the 5kHz peak.
For more TH900-like bass response, you can try GM200: