I'd try an Aurender UC100 converter, at $700 it's not cheap but you may be able to get one used. I use their UT100 usb to fiber converter and it works just great.
I'm not going to argue the pros or cons of USB sound quality, I just don't like it due to it losing connections between equipment if I jump around tracks too quickly. Every other SP/Diff connection I use simply locks onto the signal.
Best of luck and enjoy that DAC.