Rate these on order of importance:

1, 5 , 2, 4, 3.

Marco-
The Pizza analogy was great. Do you want a Smoking Loon Cab or Merlot with that pie? ;)

1 and 5 should really be tied for first--it's the interaction between the two that makes the sound. Everything else pales by comparison.

In my experience room placement is critical to getting the most out of your system. So I would start there. Once you've found a placement withint the room that works it can only get better with changing the other items on your list, though tweaking will be necessary with things like specific speaker plcaement once you change those. I've heard very modest systems with good placement kick the wazoo out of great systems with poor placement.

I agree that speaker choice is next, though closely tied in with placement of course.

The room is the biggest influence on your sound period. Do not be folled tinto thinking that the room isn't. It can make up 70-80% of yor sound. Just try one of the room correction devices and you will hear the differences. After the room the sound you prefer will come mainly from your speakers, just go listen to a dozen and you will notice that no two sound the same, ever! The equipment matching comes into play with the speaker you select. I also found that components in the same price range do sound similar some lean one way or the other as in detailed, lean, smoother, brighter, etc.

I will take mine with extra cheese and fried onions please.

Happy Listening.