Headroom started in the early nineties making audiophile headphone amps. Today they boast a phenomenal line-up of more than 20 different DAC adorned amplifiers and aftermarket cable-upgrades for just about every serious headphone on the shelf.
The Total BitHead comes with a built-in USB port which makes it a perfect computer soundcard replacement. It should be noted, however, that the BitHead uses a 16bit D/A converter. The unit comes with velcro pads to affix an iPod or another MP3 player onto it, but quite frankly it is the USB input that makes this gadget interesting. Not an analogue line-in.