If you need closed alternatives, try the ATH-W3000ANV, or W5000, or even the W1000X.
I haven't heard the other two to give any opinion, but the W3000ANV is a very worthy upgrade... especially if you value midrange.
If you can afford higher, then I think Fostex TH900 is the ultimate closed headphone.
I'm sure those are nice but I am with Sonitus in that background noise ruins music enjoyment (for me at least) and I don't think those wood headphones isolate as much as I would need. I consider the DT770 with leather pads the minimum- anything below their ability to drown outside noise is something I would not consider. That's why I am selling my K550 (excellent headphone), keeping my 2 DT770's and most likely picking a pair of these up soon (if someone has a pair they want to sell me).