Since, they are two different dacs, they will sound different. When you say "night and day" difference, can you tell me what those differences were and what kind of music you were listening to. I know that Schiit gear tends to be almost artificially punchy and fun sounding. If you were listening to Rock, I woudn't be surprised if you like the Schiit better. The V-DAC is a great value for the money. The Gungnir is 850 bucks, which puts it in a whole 'nother category of price range. Just because you find something "better"....
I don't think any one is touting the V-DAC as being a thousand dollar DAC killer. It is a really good 300 dollar DAC. You bought close to a thousand dollar DAC - yeah, it's gonna sound better. How much better is up for debate. I personally do not like the hyped up sound of Schiit products. They obviously cater to the Rock group. Yes, they are also good value for the money, but neither are they "giant killers".
I'm listening to a well recording folk/bluegrass recording through my V-DACII with V-PSUII and am just blown away by the detail, flow, and musicality of the this little combo. I really am wanting for nothing....prolly helps that it's connected to a Burson Soloist - great pairing right here, man!
I listen primarily to ambient and electronica throughout the day; rock is a rarity for me anymore.
When I say "night and day," I meant that the sound was fuller and more present, and as well I felt like I was recognizing a greater level of detail in the music. This is all subjective and take it with a grain of salt, because I didn't do extensive testing, nor do I have the vocabulary to describe what I'm (not) hearing; chalk it up to personal preference, pride of ownership, whatever.
My point point is, cumulatively, V-DAC/V-PSU II isn't cheap, and I question their performance at a $598 price point. If you remove the V-PSU II from the mix, the DAC itself can be had for as much as $349.00, which is certainly economical; then it's a matter of sorting through the arguments for or against an external power source.