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.
The headphones that I seem to enjoy the most have a frequency response that is relatively flat between 30-1000 Hz. Not ruler flat, mind you, but generally no significant variations across this range.
My Denon D5000 with J-Money pads fit this bill rather nicely, as do the Mad Dogs.
I have a friend that has allowed me to borrow his stock D7000 for over a week, and I came away feeling that there were some songs I preferred with the D7000, but overall I still preferred my D5000 with angled pads.
I realize that a frequency response graph is not the end all in sonic performance, but this is a rather important characteristic that I have found to be very useful in my headphone analysis. The W5000 looks promising, but the W1000X appears to have a noticeable hump at around 95-100 Hz with the sub-base dropping off rather quickly. The Fostex TH900 (http://www.innerfidelity.com/images/FostexTH900.pdf) looks very good as well.
That said, if I'm going to spend over $500, I would really need to hear them for a significant amount of time before I'd feel comfortable purchasing them. I initially bought the Denon D5000 because my Sennheiser HD595's (http://www.innerfidelity.com/images/SennheiserHD595.pdf) just didn't have the bass impact I craved. It was not the right sound signature for me. It looks similar to the W1000X graph. At present, I am very happy with the current sound signature of my headphones (MD and D5000). I always welcome an improvement, but I'm not out to fix anything now as I was when I first shopped around and discovered the D5000.
The Mad Dogs were initially purchased to replace my ATH-M50s in my office, but they turned out to be so nice that they directly compete with my D5000 at home, especially when sound isolation is factored in. Getting the Denons recabled now, and I can't wait to get them back to really put them to a test with the Mad Dogs.