I'm just going to post my impressions of dogears' Fostex vs my DT770-250's. Take note though, my DT770's are not a stock pair. I bought them from a head-fier a couple of years ago. They're double-entry and the cables are cryo-treated Mogami cables. I can't vouch for what the difference of this pair is vs. stock DT770's but going by what the seller told me before, the sound is more balanced compared to the initially bass-leaning stock DT770's. Anyway...
For starters, the Fostex beats my DT770s in terms of detail and imaging. With the Fostex, the separation of the various instruments is more pronounced. I could tell where the different sounds are coming from more clearly and I'm also able to hear more of the nuances in the music.
My problem with the Fostex comes from two things: First is the comfort. My DT770 cups my ears perfectly while still giving it enough wiggle room and sits on my head quite nicely. On the other hand, I find myself adjusting the Fostex every so often and simply couldn’t find the right fit. Comfort aside though, the balance of the sound just doesn’t work for me as well as the DT770 does.
I tried dogears’ current incarnation of his Fostex two ways: I initially got it from him with two pads on top of each other and a pleather wrap around them. My problem with that one is that the bass was too bloated. With my DT770s, there is a pronounced bass, but it’s as if the bass bump on the DT770 is focused on a narrower band of frequencies compared to the Fostex where there is somewhat a wider swell. The effect is that the bass on the DT770’s feels more tight and punchy while the bass on the Fostex is a bit more distended.
I also tried dogears’ Fostex without the second layer of pads and without the outer pleather wrapping. On this one, the opposite extreme happened compared to my DT770s. While it felt like the sound was able to breathe more, it also sounded a bit too sharp. So, what I’m guessing is that the ideal balance in dogears’ tweaking of the Fostex lies in between the 1-pad vs 2-pad versions.