I recently used a Sonore UltraDigital for i2s. The way this works is that it takes USB output from a streamer, such as a SOnore OpticalRendu (or anything that can output USB). The USB cable provides power to the unit.
There are 2 outputs on the UltraDigital, SPDIF and i2s. I got it mainly to use with the PeachTree GAN1 amp which only has SPDIF and no volume control. I did test out the i2s on my Musetec 005 DAC and it was very good. Though I think it suffers a little in comparison to connecting the USB of my Sonore OpticalRendu directly into the USB input of the DAC.