I just ordered the ODAC, but expect some buyers remorse as my current setup is already very good. I don't think that the ODAC will make a night / day difference in sound in other words. I already own the O2 so I am skipping this Schiit!
That said, I have to say that the $200-220 dollar Schiit stack is really competitive with the $320 dollar O2 stack (separate components / cabling). If I could have a do-over, I probably would have picked up the $285 dollar O2/ODAC combo unit or just modded myself.
Considering just how perfectly awesome the O2 is, I can't wait to see some measured performance / comparisons between the units. Then I may end up hating myself for blowing so much on headphone components (almost as much as the phones' themself - Doh!). But I know the O2, if it lasts, is going to be a great amp for all future phones' as well.