Though I think that DAC's would be less of a concern in terms of audible improvement: there's only so much of 32 bit 192khz conversion which can be done, and so much output circuitry one can do.
I have read from from a review that the bifrost with uber was more resolving than the ODAC, with the 650s, but wasn't the improvement they'd expect for the difference in price.
Some even have said that in terms of neutrality, there's no benefit in upgrading to the benchmark DAC1 from the ODAC.
I would totally spend the money to see if these claims are rightfully so, but alas I have no funds. With the general consensus that the DAC reaches diminishing returns much earlier, this becomes the reason why I am very much interested in the Crack as the next pairing to my HD650's.