It looks like this one’s been out there for a while, but it doesn’t make it any less awesome. [Andrija] built this combination portable DAC/headphone amp. It takes optical audio input, feeds it through an analog devices AD1866 16bit/96khz decoder. After that, the audio is brought up to volume by an op-amp style headphone amp circuit.
Side note: I wrote up a few short notes on the Sidekick LX I got today, if you dig that sort of thing.