AKG has recently brought out their K601 and K701 models. Both of these are more than $200. But the good thing is their excellent K501s have become really cheap. You can get some for about $125, if you find the right deal. They're well known for their exceptional midrange. They're often identified as having slightly light bass, but depending on what he's mixing, that may not be a big deal.
They are open, though...that may not be good for him.
Sennheiser HD580s are also a good bet, probably for around $150. And you can often find the HD600s for close to $200, especially if you buy lightly used ones on head-Fi.
head-Fi is your best resource for headphone info though.
Chad