I'm hesitant to make a direct comparison with the Yggy, because it's been over 2 years since I owned it, and when I did it was with different amp and headphones. That being said, on sound alone, I'd probably still prefer the Yggy slightly. I think the Yggy is more sonically well-rounded. The Gumby is a little different because it has a warmer overall signature than both, but the strength that I find with the Gumby is that its very well rounded and doesn't really do anything "wrong" per se. It's a safe choice in regard to equipment pairing. Both of the Schiit DACs tend to have better bass depth and detail, but that's one of their strengths. Depending on a person's tastes or other equipment, they may find the Qutest or even the Yggy to be too bright or aggressive, though I don't think that's the case myself.
The other reason I wanted to wait a bit longer before making more definitive statements, is the difference with the stock supply, and using the iUSB. I went back to the stock a second time today. While we're well into diminishing returns on DACs, I'm currently thinking that if I did not have the iUSB, I might have ended up deciding to sell the Qutest. It is a somewhat subtle difference, but enough to push the Qutest into what I would consider to be the next tier up. EU prices are of course a different value proposition, but in USD I'd probably be willing to pay no more than $1500 for Qutest in stock form. With the iUSB (at $200) I think it is just worth the money together ($2100 U.S. combined retail). Given the EU prices on Schiit products, the Qutest + iUSB or similar would probably be a better value.
I realize that is kind of bold statement, which is why I wanted to wait a little longer to say for sure, but that is how I'm leaning right now. The iUSB isn't a night and day difference, but it's just enough to bring out some of qualities that I expect from a truly high-end DAC. Without it, the Qutest seems a bit flatter in soundstage presentation, with less distinct microdynamics, and a certain "grayish" haze going on with the texture and timbre range of the treble. Please note however, that my house is likely a mess of RFI, with lots of cell phones, tablets, computers, and other wifi connected devices, which the iUSB likely cleans up on both the USB power and signal lines for the Qutest. Less polluted homes may fair better.