Why'd you rule out the M51? Just curious. I picked one up on Audiogon after selling my PWDII, and I'm honestly starting to wonder if I have any ear for these things at all, because the differences are minor. I wish I had the time and the funds to have more than one at a time.
I rank the ones I've tried like this:
1. BMC PureDAC
1. PS Audio PerfectWave DAC II
2. Gungnir (gen 2)
2. M51
3. Yulong DA8
3. Bifrost (Non uber, gen 1)
The differences between the 1s and the 3s is probably about 5%. The only real standout is the gungnir, which has a definite liveliness that the others don't... I guess I agree with Purrin's assessment that it's very dynamic. I liked it, but more with the LCDs and Mjolnir than the WA2 and HD 800... of course the one I used with the wa2 was a gen 1, so who knows what that means.
Nothing about my comparisons is scientific, and my results are not particularly revealing. I didn't have the same amp or headphones for all of them. I tried the Gungnir with Mjolnir and with a Woo WA2, the BMC on its own, the Yulong with a Mjolnir, Bifrost with Lyr, and PWDII and M51 with Eddie Current S7. I've gone through 3 LCD2s, an LCDX, a T1, and two HD 800s.
I'm about settled on getting some speakers and calling it a day.