James:
All good questions, answers will have some logic and some just because I am bit crazy and went over the top (and like it that way).
Screen to sofa is 14'. The entertainment area is in one corner of a much larger open space including kitchen/dining/living/family. When we remodeled, we decided to remove the walls and have one large area that flowed together. The entertainment area is roughly 18' x 20' with the whole open space being roughly 36' x 42'. The idea for the entertainment is that music and movies/super bowl could be clearly seen/heard from just about anywhere in the entire space.
Ahhh, the 533s. Originally, I ordered a 6 series system and later after hearing the 533-T decided I wanted a pair for the study (separate part of the house) to listen to music. Once I got everything, I couldn't help tinkering and wanted to see what they would sound like in the main entertainment area in combo with the 633-T. As it turns out, I really do like the combination, in particular for music. I am still experimenting and have not decided when/if I will move them to the study. To answer your question directly, no I did not think anything was missing. But I must say the mid to upper mids are fuller with the 533-T combo (why I like it). I don't think it makes much difference for movies.
2 centers - a couple of reasons, 1) I had often read that when you have a large open space that two centers can help give better definition to the dialog. the recommended configuration is to have one just above (tilted down) and just below (tilted up) the screen converging on the main listening area. Unfortunately, the ideal set-up wasn't practical in my case hence why I ended-up with what I have (works better to fill the entire room anyway). 2) Unfotunately I have a slight loss of hearing and always found the dialog to be difficult to understand, especially in movies with large dynamic ranges (whispered dialog to large crashes/explosions).
633 surrounds - there are a number of issues that came up that led to this decision 1) there aren't any walls to hang speakers on, (large picture window on only wall side) 2) hanging from ceiling in middle of room was unacceptable to wife and would block views 3) in ceiling was unacceptable to me (just did not like the sound for surround and especially not for music) 4) I looked at several stands, but the costs for what I liked was not much different than buying the tower (stand + 632 close to 633), 5) overall footprint of stand and speaker not much different than tower 6) Liked the look of the tower versus book shelf and the stand. In case you are wondering, I wanted direct radiating speakers for music (just prefer them over dipole/bipole). The loudness is not an issue, just tuned accordingly. Closeness is an issue as you described. The rears are a few feet behind and are fine but the sides are close so that if you are at the end of the coach you are within about a foot and does not blend well (the center of the coach on the other hand is awsome). But bookshelves would have had the same issue. I will be experimenting with different layouts in the future subject to wife constraints
Nothing is in parallel or series for that matter so there is not any load issues. Each speaker has its own amp. Seven channels on 4306 in normal config and I then use the pre-outs of L/R/C to the monoblocks (same as what you typically do for a powered sub (low level sub pre-out)).
If anything is not clear, just ask.