The sound signature between the HE400i and HE560 is not an incremental difference to me, its different enough sound that I keep both of them. I got both at the same time with the intension of sending one back but with the first listen of both they were quite different. Also, I paid $450 for my HE400i and $720 for my HE560 but this was back over 3 years ago when they first came out.
^^This! I'm also keeping both and I honestly find the signature on the two to be quite different, a lot more than what I'd call subtle. As always YMMV...