Those statements really make me want to hear the fostex. I owned a pair of la7000 and thought overall they improved the stock d7ks in every aspect. But a couple of things the la's didn't fix were the grainy mids and harshness in the lower treble. I sold them soon after getting the w3000. Now since you find the fostex better than the at's then they much be a pretty big leap over the la's.
Now to the 7100s, you can get them for around the 700.00 mark which might make them attractive. I own the d600 and find their performance to be better than the d5000, but not quiet up to the d7ks, but close though. But again, there are many who find the d600s to be better than the 7100s though. But at 700.00, they might be worth a try.