So, I wanted to comment again on the 4490 now that I've put a couple of weeks into it. The sound, to my ears, has really smoothed/mellowed out. I'm not sure if it's actual product burn-in or brain burn-in, but the result has held for several days now.
The sound is not as lively and energetic as it was when I first got it, but it sounds more coherent and less fatiguing. In short, it sounds just that much closer to what I remember from the MB Bifrost.
I'm digging it.