What do you do with the shielding? Do you just ground it to one side? What happens if you have separate sheilding for the power signals and data signals?
You absolutely must connect the shells of the USB plug ends (the metal shell) to each other, generally it is done using the overall cable shield. If you don't, you can brick your DAC. You can put a separate shield on the two data conductors and the two power conductors. Then just connect both shields to the metal part of the USB on each end.