I guess its my turn to spill my 2 cents...
For the Octavarium image (the star in the octagon pic), its clear to me that its an architectural layout diagram, like something done in AutoCAD for building layouts. It seems that on each of the directional sides (north, south, east, and west faces) of the octagon are what is usually a symbol for doors in these types of diagrams. Only one of the doors is open (the south face), maybe symbolizing the whole notion of starting off the story where it ended. You enter through the only open door (the beginning of the CD)and have to make your way around the Octavarium, and when you get back to where you started, you can choose to leave and move on, or you can repeat the same cycle again, getting trapped in the Octavarium.
I dunno though, to me I get a feel of a lot of the whole "viscious cyle" type feeling, as kinda stated in my little theory above. A lot of the songs have a theme of repetition. In Root of All Evil, you have someone caught in a viscious circle of addiction, trying very hard to get out. Answer Lies Within shows perhaps a key to escaping the octavarium, while These Walls sort of represents many of the things which prevent us from moving on with our lives. I Walk Beside you is another close person trying to help the trapped person escape. Panic Attack is a person very jittery about things, perhaps due to paranoia from 9/11 about terrorism. Never enough is about Mike taking a giving all these things for the fans and getting the short end of the stick, but continues falling into the same pattern and coming back to the fans. Sacrificed sons obviously is about the circle of violence in terrorism, in the sense that zealots commit these religious based attacks and yet it keeps inspiring more and more people to try these attacks out in the name of God. Just some random thoughts. Also the cover is one of those balls that always cycle back and forth, more symbolism
I also get the odd feeling of this being a "Goodbye" album for some reason. Never Enough was some pretty heavy feelings (anyone reminded lyrically of Tool's "Hooker with a Penis"?). The eight ball is always the final ball to be sunk, the stop sign, the fact that the cover ball isn't going to hit any more balls...I dunno...all their various styles seem to converge on this album, from the heaviness of ToT to the some of their experimental type stuff from Great Debate, to their Images and Words/Awake type stuff. All in perfect balance...ready to leave the Octavarium...
Of course this is coming from a college grad student who hasn't eaten anything in a day, and had about as many hours of sleep in the last 4 days as I have fingers on my hand...so if this is complete garbage, don't mind me
