After some serious listening sessions I've come to some conclusions about my s400's. First let me say I'm a novice when it comes to head-fi so these are certainly my personal preferences and not some highly experienced and analytical review.
I definitely enjoy these headphones. Their isolation is good. I found an extremely comfortable position, but then learned it's not the best acoustic position so I'd say with sound quality in mind they are about a 6/10. They have nice detailed highs, sometimes a touch strong but easily EQ'ed and I'm sure better after a burn-in. Lows are solid, but I don't have the experience, let alone the words to describe their qualities. For me they provide the punch I want and reasonable deep tones (wording?) and once again respond really well to EQ. The mids are, in my opinion what needed the most work. It seemed to me that right around 1K they were overly strong, giving lower register vocals too much power and making them sound muddy. Then immediately following there seemed to be a big drop, making mid register vocals sound distanced and weak. I gave a 1 db drop to the 500Hz freq range, 3 db drop to the 1KHz range, then a 3 db increase to the 2KHz range and a 1 db increase to the 4KHz range (all in poweramp on my phone). To me that gave a sound signature I really enjoyed, and after a lot of experimenting decided it worked for all of the genres I listen to.
I put these through the entire Rolling Stones 500 Greatest Songs of All Time, Doobie Brothers Best Of, Eagles Best Of, 90's Underground Hip Hop, and various country, pop and electronic music I've collected, all in FLAC format directly connected to my phone.
I also have the KSC75's with a cmoy amp using the RA1 JR4556 opamp and since someone asked earlier I'll quickly mention that with the above adjustments (these phones don't seem to benefit from the "warm" sound that the amp provides) have close to the micro detail the amp/hp combination provide. I still prefer the open design for rock and natural instruments, but I am SO pleased with the combination of isolation, bass, treble detail, and cost these things provide. For 45 dollars I have a great rock/quiet environment combo, then for 27 dollars I have a great pair of travel phones that do so many things well. If that isn't budget-fi I don't know what is. I plan on grabbing a couple opamps that are supposed to be better for soundstage and mid/high detail to test with the s400's to see if I can amp them successfully to my liking.
Anyways thank you to Ghost and everyone in this thread. So glad I made this purchase.