I passed on my Yamamoto to Joel Chevassus on staff so I don't know how the YDA01 would stack up to the current crop of DACs I've had through.
What I do know is that Joel compared his Yammy to the fully discrete French R/2R DAC by Vince Brient. Vince sent me the same DAC for a 2nd opinion. There I had a chance to compare it to the Metrum. It was very much the same flavor but the Frenchie perhaps had the slight advantage. That makes me think the Metrum surpasses the Yamamoto by triangulation - but that's just an (educated) guess.
The U3 improves upon the OEM hiFace built into the NWO-M; upon the USB receiver of the Burson DACs; and even the Zodiac Gold (arguably the least on the latter but still audible).
There will probably be DACs that *won't* benefit from the U3. And there probably are other USB-to-S/PDIF boxes like the Audiophilleo, KingRex et al that match the U3's victory lap of improving high-quality DAC with good USB implementations.
I'm not sure yet *why* the U3 works as bloody well as it does. The XMOS chip inside is apparently very trick. But the real 'magic' could be that, A/it's external and B/ that it's bus powered. I noticed that designer Simon Lee didn't integrate the U3 into the mother board of the Eximus DP1 I currently have in for review but left it separate (piggy-backed) though obviously in the same enclosure.
I'm usually more in favor of integration and less cables. With the U3, I stand corrected. The Yamamoto of course has no USB input so the U3 or something like it becomes required for streaming files. I was simply surprised that the U3 would be superior to what's inside machines of NWO-M/Zodiac Gold stature (i.e. *everything* I've got in house).
There's probably something going on we don't know yet. Other listeners have posted similar findings elsewhere with Steve Nugent's equivalent interface...
