http://headphones.exblog.jp/ had some a comparison between the blue and the black awhile back, but I can't seem to find it now(I'm a little sick, maybe it's right there, and I'm not spotting it). It looks like the post was edited a couple days ago, and they're only talking about the software upgrades. Maybe someone with better Japanese(and without a fever) can take a look.
In any case, I remember the reviewer found some differences between the blue and the black. I don't even want to try to remember exactly what they were right now, I'd probably misquote him big time. Lavry himself commented that he thought the sound would be very similar or the same, but it turns out the two have major architectural differences. Take this with a grain of salt, but IIRC the author of the blog found the black used a single stereo dac IC, whereas the blue used a separate stereo dac in differential mode for each channel; i.e. each channel was output in positive and inverted polarity using an entire stereo dac, and then recombined later. This was done to decrease cancel distortion in the dac IC, but it seems to have been abandoned in the black. Maybe it didn't make a big difference, or combining the two phases was detrimental to audio quality. I believe the combining was done by an already present amplification stage, as to not add another stage in the signal path. This was independent of the balancing of the DAC. Again, fever, bad Japanese skills, grain of salt...