There is no doubt there is comb filtering in 2 channel playback. The tests Shawn recommended do demonstrate it. And I realize that you prefer the multi-channel reproduction of music.

I find myself coming back to 2 channel reproduction and live with the comb filtering just as you say for much of the music to which I listen. I do listen to different tracks in both PLII and straight 2 channel. Most often, when level matched, I tend towards 2 channel unless there are predominant vocals in the song. I think I get a more precise imaging with 2 channel. But that could be all because of room acoustics.

Ain't it great we have options though?