Back to the question the original poster asked. Here are extensive measurements of the DACMagic. Here are the specifications from the manufacturer. I haven't seen any measurements of the Bifrost, and their product page does not have many specifications or measurements posted. Are there any detailed measurements of the Bifrost published?
I haven't listened to either of them, but if I was buying without getting to listen, I would definitely get the DACMagic Plus. I don't understand why some companies don't publish measurements of their products, or at least detailed specification sheets.
Try USB from your PC if you get the DACMagic, it should work better than the digital output from the PC because of jitter and noise issues.
Just my 2 cents.