Sorry, I haven't had time to go back and re-read (and re-absorb) the original report. If I recall correctly--and perhaps I don't--the computer-based A/B switching apparatus didn't have a channel suitable for DSD input, so some means of multiplexing the bitstream was devised, with the signals then being reassembled on the other side. I'm really sorry since I know that raises as many questions as it settles, plus as I said, I should re-read the thing and not go by memory. But I am very pressed for time these days so realistically, I probably won't get to it any time soon.
FWIW when I did the translation, I was emailing back and forth with the two authors of the study a fair amount, and nothing caused me to doubt the integrity of their experiment or their interpretation of the results. I learned some useful stuff from them on the interpretation of experimental data, too. Their article was on its way to being published in the Journal of the AES when unfortunately, a technicality caused it to be removed from consideration: Since this was essentially a master's thesis, it was required to be published in Germany, but the JAES requires that their articles be previously unpublished. (Shaka, when the walls fell.)
--Just this morning I got a mass mailing from Benchmark with a link to this blog article in it:
http://benchmarkmedia.com/blogs/news/41262017-audio-myth-dsd-provides-a-direct-stream-from-a-d-to-d-a. On a quick first read, I think that it's accurate; occasionally I find what looks like commercial bias in this author's postings, but what he's saying here seems apt. What he doesn't say is that the expiration of certain key patents from the early days of the CD format, and the ease with which people could "rip" tracks from CDs, were significant motivating factors; the attempted (and not very successful) introduction of DSD was the behavior of a company trying to preserve its revenue stream by means of planned obsolescence--whether or not that was in the interest of the public or the rest of the recording business.
--best regards