i tried to supply my hiface with 5V battery power, but i didn't notice a difference.
Actually i hoped that it would lower the noise floor a bit. I have a clearly audible hiss as well as a hum with any device i have (hiface, monitor 01 USD, esi maya 44 soundcard).
My other sources don't have this probelm. The dac is silent too when i disconnect the spdif cable.