The HE-400 should make a great basshead can that have enough soundstage to spare but they're fully open phones. Best soundstage from a closed can I've heard so far belong to either the Denon D2000 or the Kenwood K1000. Unfortunately the Denon is discontinued and becoming harder to find while the K1000 isn't exactly for basshead. If you want to go the Ultrasone route, I've heard both the Pro 750 or Pro 2900 would be a safer choice than the Pro 900.
Depending on your purpose though, the Denons are closed back but leaks a lot of sound. I currently use the DT770/80 as my closed back, and like them a lot. I have the Alpha Pad of the Mad Dog coming in soon though. I believe that will be a nice upgrade with great isolation and sound leakage protection too.