I bought Oppo HA-2 headphone amp recently and it sounds amazing. It has asynch USB, SPIDIF, DSD an analog in/out. I use USB. Sounds better than my Benchmark DAC1. D/A converter IC is SABRE 32-bit. It has lithium battery and can be used with a phone, but I’m using it as stationary unit only (next to my computer).
https://www.oppodigital.com/headphone-amplifier-ha-2/
https://www.oppodigital.com/headphone-amplifier-ha-2/