A very brief write up of my experience, just before I am off for a week of wintersport, so remarks and questions will have to wait a bit for my answer.
I compaired two sound cards from Onkyo , the 90 and the 200 ltd, and each with 44.1 files and with quad + arc prediction.
I used both speakers (ob Hawthorne enabled and ob subwoofer with 5 15 inch drivers per side) and headphone (UE 10 custom, really great !).
I am not really good in wording the impressions I have and the observations are biased by my preferences and equipment of course.
The cards were very new and I really had to let them warm up for a few hours after swapping them in and out. Only one slot available unfortunately. The 200 sounded really horrible when cold, that did not change in these weeks. The 90 was less effected but also soundend better after a couple of hours of use. Maybe this will change with more weeks of usage.
I used a set of 8 songs for the comparison, going back and forth over the days and diiferent setups.
I think that the just stereo and cheaper 90 is at least as good as the more versatile and more expensive 200 ltd. With the 90 it occurred quite a few time that I forgot the task of judging and was just listening and starting other albums instead of the set of test songs. The 200 was less involving and fluid , imho.
And for me the quad and arc was really superior to the 44.1, more three dimensional feel of the instruments and more realistic small details, that for me are very important.
well Fidelio as I think you mentioned that the quad+arc for you is worse than the 44.1 files, you probably will doubt on my findings about the 200 card. Sorry about that
Leo