I've seen some adapters(isolators) for reduce jitter for pc stuff like sata hdds or usb. But lost store's link. For usb I've found (ADuM5000), but for sata didn't. Have you seen it?
I just bought handmade DAC with musicland's usb receiver, that don't support linux.
DAC has s/pdif input too. I thought to buy usb to s/pdif convertor, but didn't find one compatible linux in small budget (