Thatonenoob posted a review of the HUD-DX1 DAC/Amp on Head-Fi. According to the review it is a pleasant sounding unit with optical input and RCA line out. This is unusual for sub-$400 portable DAC/Amps. It also support DXD/DSD native.
Pros: DSD/DXD Capable, Musical and Engaging, Nice Trim
Cons: Gain Switch Lacking, True Lineout, Not Airy