Been a while since I've posted on here, but in case anyone is curious I have had the signature djs for 3 or so years and the fostex th900s for about a year and a half.
Right now you can get a th900 for around the same price as the djs, and all I have to say is that if portability and sound isolation arent 100% necessary then get the th900s. They sound better, lol. If the th900s sound quality is a 10, a sig dj would be a 6.5.
Granted, I do enjoy the sound signature of the djs a bit more. The djs have pretty much the perfect sound sig for me - compared to the th900s they have less treble and a bit more midbass.
Keep in mind I still am driving both hps unamped, and considering the difference in sensitivity I imagine the th900s still have a ways to go as far as sq.
Besides that though, the th900s just sound better. The clarity is insane, the soundstage is massive, and everything just sounds more real to me. The sub bass has a very visceral, textured sound that I just love. Can't even compare the instrument seperation. Not to mention that these are the most comfortable headphones I've ever worn.
Anyways, just thought I'd pop in and give my two cents, the djs are still great and worth the money if you really need sound isolation and portability, and the soun signature is perfect to my ears, but the th900s just sound like another level of headphones to me.