The DACmagic + using it's own ASIO driver is Cambridge Audio's reccommended set up, but the amount of noise interference from te laptop is disturbing. The optical connection is much quieter, but sound softer, a little less dynamic. There's no more sibilance or harshness that might be attributable to more jitter, just seems a little flatter, less exciting somehow as if the grilles have been left on the speakers.
Is this similar experience with other DACs? I've read that the NAD C390DD sounds better via optical than USB unless there is an Empircial Audio Off Ramp used between PC and amp (not figured out yet what this does the J River doesn't do with the Dacmagic anyway in USB async mode....)