PS Audio offers I2S input over an HDMI cable, and there are some other manufacturers as well who use this. It's a way to transmit DSD into the DAC without the USB issues. Gd audio make sure the connector, http://www.audio-gd.com/Pro/diy/I2Skits/I2SEN.htm
It it would be amazing to have a preassembled (and tested!) board. I know the potential sales volume might be lower, but anyone with a PS Audio or similar audiophile product would probably be willing to pay more than $50 bucks for the board, I know I would!