I use a Wireworld Ultraviolet usb cable between dac and mac mini,weather it is better than a stock usb cable is highly debatable! It does however isolate the power conductor which must be a good thing. But it is a very well made cable with good, strong and tight connectors at either end and I figured spending about £40 was a worthwhile and relatively cheap investment on £1500 worth of dac and mac mini!
I honestly don't know if it makes any difference to sound quality,it probably doesn't,but as I said it's a relatively cheap investment and I feel better that it's in place instead of a cheap stock cable.
Andrew.