As it happens I was just doing some more intensive listening with the 8801 last night and figured I would see if I could notice the difference between using the HDMI input and 2-channel analog inputs. Perhaps not surprising (though I guess it was a bit surprising to me), I definitely noticed a difference in the character of the sound. I played a CD using my Lexicon RT-20 which was connected to both the HDMI input and the CD analog input and had the 8801 hooked into a Bryston amp using the balanced connection. I did not do any setup using Audyssey and was listening both in the music mode and the direct mode (which didn't sound noticeably different). At first, what was clear was that there was a volume difference and so every time I switched back to the analog connection I had to adjust the volume up a bit to keep the same overall volume (not sure why) and also at first I thought I much preferred the analog connection but after going back and forth for 15-20 minutes using the same 20 second part of a track, I realized that they were just different. The analog connection seemed to be more airy and transparent and the HDMI connection seemed to have more weight/presence (if that makes sense) but seemingly less transparency - at least at first, until I realized (or convinced myself) that the same details showed but with a bit different style.
Am I right to assume that with the HDMI connection the Lexicon was not doing the processing/conversion and the 8801 was and in the analog connection the Lexicon was and the 8801 was just passing through the analog signal? I thought perhaps it was just a difference between the Lexicon and the 8801 but based on the above post, perhaps there is something else to it. I wouldn't have described the analog as tinny or harsher but I definitely understand the not as rich or full comment.
As a side note, the further listening session confirmed my initial impressions that I like the 8801 and shouldn't have an issue moving from the Anthem to the 8801.