I think your experience would have been better in a traditional RealD 3D theater versus IMAX. Unless a movie is shot entirely in IMAX I don't think it makes all that much sense to go see it. The 3D scenes were very blatant to me but in a good way and almost slightly annoying when they would...
Actually your statement isn't entirely true. I know for a fact the Blu-Ray version of Pan's Labyrinth is indeed a 7.1 DVD. The point is though, 7.1 media is very scarce and you probably shouldn't really worry about it. 5.1 or 6.1 is plenty for any home theater from low end to high end.
I use a Sony BDP-S300 with my 3803 and love it. I just use the analog outs as you're thinking and feel the lossless audio is superb. I will be waiting a while to upgrade my receiver and dvd player at the same time for 1/2 the price and all the features.
I have not had this issue. BR lets you switch tracks in the middle of the movie and the optical 5.1 track is just as loud as the uncompressed track through my analog outputs. I'm sure it's different from receiver to receiver though...
You have to use 6 RCA cables which run from the analog outputs on the BR player to the analog "ext in" inputs on your 3803. It's one cable for each speaker in the 5.1 setup. Check out the back of your Denon and you will see a section of inputs called "EXT IN."
Hmmm...I thought that mode was used for 2.0 tracks? I have used a 5.1 setup forever so I just don't keep up on all the crazy 6.1, 7.1, etc modes used...