Joshnor713 posted a review of the micro iDSD DAC/Amp on Head-Fi. It’s quite large but has capabilities and i/o not seen in other devices in the $499 price range. You can even charge your phone with its battery.
Pros: Clear, detailed, full, and engaging sound. Huge battery and smartphone support. IEM sensitivity matching, bass and 3D boosters, various audio formats
Cons: It’s large for a portable DAC. Smartphone cable is not included.