I've been going back and forth between the V800 and HDVD 800 dac a lot and I just can't decide which I prefer. The huge soundstage of the V800 is nice and there's a few tracks where it's definitely more detailed than the HDVD dac. But at the same time the V800 just sounds a bit boring compared to the HDVD, which just seems to come out with more dynamic impact across the entire frequency range. I don't know how to describe the difference exactly.
I've also done some tests with Dolby Headphone in games and movies with a Asus Xonar Essence ST connected via coax. The more precise soundstage presentation of the HDVD dac won out there, as it was easier to pinpoint where the sound was supposed to be coming from, while the V800 was a bit more vague. Dolby Headphone in general sounds mediocre, as I don't like how they do the simulated room acoustics, but with the HDVD 800 I enjoyed it a bit more than I've done before.
One thing that's for sure is that the HD 800 sounds just fantastic with either dac. For a couple days I listened with the LCD-2, and when I went back to the HD 800 the improvement in fidelity almost came as a shock. I used to think they were somewhat equal in many respects, but now with a proper amp the HD 800 shows just how much potential it really has, while the LCD-2 seems to hit the limit of what it's capable of. It still has a nice polite balance, but in terms of fidelity it falls short. It makes me want to get the LCD-3! I like the LCD-2 style sound, and now I want it in higher fidelity so it's a viable alternative to the HD 800 again.