The first is that the Bifrost seems to very detailed and revealing, but I find that the highs are pretty aggressive and on the edge of inducing listener fatigue. I can tell you that the first hour of play, it was pretty dreadful. The sound presentation is also thinner and not as full-sounding, though the imaging seems to be pretty fabulous. I find there's a bit a "relentlessness" quality to the Bifrost right now that is a bit hard to take. I did find improvements already by the 3rd or 4th hour mark, but I'm still hearing things I don't like, notably the brightness and "relentlessness". I find the sound to be a bit smoother with the SBT with optical than the asynch USB via the Macbook and AIFF files.
What can I expect with regarding initial experiences prior to burn-in, how do things change after burn-in, and what are typical burn-in times that folks are experiencing?...I'm guessing 100 hours or so will be required before you can really judge the merits of the Bifrost. I've read some of the post here, but obviously receiving the Bifrost last night I haven't had time to read 135 pages of posts.