Edited by giedrys - 6/18/12 at 11:28am
I think that''s more to do with the quality of your usb chip and transmitter compared to the spdif chip/transmitter. Though I was never a fan of usb DACs myself (I'm sure the newest hires asynch usb dacs may change my mind though)
Oh, and you should have all your digital volumes set to max. If you're worried about volume then control your main volume as needed.