I don't have the Gungnir, but I do have the Bifrost and the Yggdrasil. Yggy was a big step up from Bifrost. But it is huge and not very desktop friendly, unless you have a really large desk. I recall reading reviews on Head-fi comparing Yggdrasil and Gungnir and some people preferred Gungnir.
Just a thought: with the money saved on a Gungnir, you could build or buy a dedicated music server/pc w/ linear power supply. I've found that music players and their power supplies -- i.e., everything that comes before the DAC -- have a plainly noticeable impact on sound quality.
cheers, Derek