I received my USB equipped bifrost yesterday too. Especially exciting as the tracking suggested that I would get it today instead.
I will let it burn in for a while before forming any opinions on it but I agree with what others have said in that it is significantly nicer than the Cambridge DacMagic. I tried the USB using a silver usb cable playing 196 delivered source from Pure Music software and it certainly doesnt sound bad at all. I think that it may add extra weight to female vocals but the optical, even at only 24/96(limited by the MAC), is cleaner sounding. This is just my quick thoughts from an initial listening session so I cant say that they are confirmed as yet.
The interesting thing that did go through my head though, apart from glorious Schiit delivered tunes, was that I was thinking of my need to upgrade further. I was sitting back thinking that Mac, Pure Music 1.85, Bifrost to Lyr to Hifiman HE6 was a great combination. How much extra quality could I get for the money? Then I thought....Gee Jason may have done himself out of future sales by creating his entry level products that do such a fine job. I was very happy indeed with my current rig.
Luckily....senses kicked in an hour later and I thought...yes the volume could handle being run at 10-12 rather than 12-2 and I wonder what Jason's uber Dac will do if this is the base model.... I am hooked in...again!!