I've heard (and reviewed) Bifrost but not Gungnir. It is definitely neutral, with a slight tendency toward a lighter, brighter sound - clarity rather than warmth. The above-mentioned reviewers also note a slight mid-bass bump and possibly a touch of top-end sibilance - both of which Gungnir does not have they say.
Wow, that's great. Thanks so much. Interesting that the gungnir more than held its own against DACs costing significantly more. As always, there's no substitute for a home demo, but it seems like the gungnir is definitely worth auditioning. (It's also the DAC I really WANT to like, as the guys there are very responsive and I love the idea that it's upgradeable. Technology is moving so quickly at the moment in this area that this is a huge plus for me).