I must say I'm completely pleased with the sound signature of the HE-400s. Dare I say... I'm content! But I need a closed-back alternative for when open cans are just a bad idea. I'm leaning towards the Fostex t50rp and following the mod guide (seriously, what better way to spend $100?). But there are other offerings out there that have advantages. The Sony MDR-1R looks quite nice are are said to be very comfortable. I've always been a fan of velour Beyers, but can the Custom One Pro can stand up with the HE-400s mids? And then something old or new from Denon perhaps? Can't cost more than the 400s, he'd definitely get offended.
I don't expect a twin, but I'd like them both to sound like they came from the same parents, you know? I'm open to your ideas and, more importantly, your experiences.