Unfortunately, I feel the USB input is just "that bad"...........It seems as though it was put on the V800 for convenience purposes.
Using the USB input of the V800 made me regret buying it, full stop! The Bladelius USB DAC which I also have, was all over it at half the price. I was even getting a better sound using the line out of a DX100 sourcing the V200!
It wasn't until buying the HiFace Two and using the coax input that the V800 showed itself as a quality DAC. In concert with the V200 and providing you have matched the cables well, it truly is a wonderful set up at it's price point. I am really loving it at the moment, with all my head phones and IEMs.
IEMs on the V200 sounds awesome, I have W4, 535ltd, 2 pairs of Hybrid DD with 2BA and a monster 20 BA,10 BA per side IEM. No hiss, just black backgrounds...................simply fantastic sonics.
With Cans, the V200/V800 combo is just as impressive. With lots of matching of cables, i/c and power, I have managed to get a stunning sound out of the LCD-2 and the HE-500, both on silver/gold hybrid cables.