Hey, I work for a place called HeadRoom (headphone.com) and we manufacture headphone amplifiers. They are a little pricey, I'll give that, but very honestly they are of good quality. The lowest end line has a plastic enclosure, but you can get one with a built in usb dac for $199, and we have a 30 day return policy if you don't like it.
I totally realize I probably sound like a corporate shill, but I'm just trying to help out. And, by the way, if you ever look to upgrade your headphones go with the AKG 701s. We have demo pairs of every headphone we sell that the staff can listen to and almost every single person there prefers the 701 to everything else we sell.