For headphones I cannot help you. I have never hooked up the Yggi to the headphone amp section of the R28NOS to test the internal R28NOS dac and the Yggi. With speakers though when I still did have the Schiit Kara as a preamp, I hooked up the Yggi for a few days to my gaming/tv/music set up then I hooked up the R28NOS to the Kara for the same use and the Yggi was easily an entire couple levels above the dac section of the R28NOS, it was obvious within seconds. Everything we love on speakers, soundstage, instrument placement, dynamics, all of it was way better on the Yggi. I still LOVE the R28NOS for speaker set up. That is what is on my speaker room right now. The preamp out on the R28NOS in fact is so good and the Schiit Kara is so transparent (props for shiit for making a great preamp) that I sold the Kara and just have the R28NOS as the dac/preamp for my speaker amps. The only comparison one can really do between the Shiit Yggi and the R28NOS is of course comparing the dac section only and yes the Yggi is on a whole other level for me when compared to the dac section of the R28NOS. It's almost unfair to compare the two.
That said, in my nicer headphone listening zone I do have the Yggi hooked up to the Audio-GD HE9LE. That combo is wild. That is the closest comparison I can do for headphones for the R28NOS but the problem here is that both the dac and amp in this comparison is far batter than the dac and amp combined to make the R28NOS. In the Yggi HE9LE combo the soundstage is so realistic and open in all directions that i sounds like it is showing me parts of the rooms in which the recondings were recorded. There is a dimenstionality to old songs I have listened to for years that I have never heard before. Its like I can hear the artists in the room almost. The R28NOS in all its awesomeness doesn't do that for me, not even close. For a time I did have the Audio-GD - R7 MK2 dac connected to the HE9LE. That was fantastic but I still like the Yggi OG connected to the HE9LE better. It's not because I like the Schiit house sound better than the Audio GD house sound. I don't. It's the specific synnergy between the Tggi OG and HE9-LE that I love. I had the Bifrost 2/64 connected to the Schiit kara and that was rad and fun but the R28NOS in place of the Bifrost 2/64 + Kara is WAY more realistic and organic and that's what I want for my speakers.