Hope I am not too late. I did the A/Bing over the weekend. Overall the differences were so negligible that, if you said the differences were all in my head, I wouldn't argue with you. So here are my (quite possibly strictly psychological) impressions now that I have more experience with USB vs Optical/Coax:
1) Keep in mind that due to how the EMU-1212m works (my optical/coax source), I must lock it at a certain sample rate/bit depth, I chose 96/24, so if its not 96/24, JRiver resamples it on the fly
2) On tracks that are below 96/24, I felt that the USB in native sounded a lil less harsh than the Optical locked at 96/24.
3) On tracks that were at 96/24 exactly, the optical might have sounded a little cleaner.
4) On tracks were above 192/24, I could tell no difference between the downsampled Optical vs native USB 192/24.
So, if you have an optical/coax out that is capable of changing between different sample rates (vs something that MUST be locked to a sample rate/bit depth like the EMu), and especially if your optical/coax can do 192/24 and you were limited on funds, DEFINITELY get the Uber Analog upgrade over the USB. In fact, do this anyway. I never heard the Bifrost w/o the Uber stage but from what I've read, its the upgrade that really makes the Bifrost sing. The USB is worth it if it's the only way you have to connect the Bifrost. If optical/coax is an option and you only have the cash to spend on one upgrade, do the Uber! You can always do the USB upgrade later is you're really curious, its easy as pie to do yourself.
Thanks for that info BruinAnteater. That helps alot. That is most likely what I will order, the Uber w/o usb. My dilema now is that a friend recommended another DAC, the SimAudio Moon 100D. 350 @ MD. Still researching, but leaning towards the Schiit...BTW, I'll be using mostly Macs for source.