And to round out the anthology...
Second edition:
Goals and Tools
When considering the purchase of components for a sound system, it can be useful to think of each component as a tool: you need the right tool for the right job. To that end, you first need to start with a goal: what are you trying to accomplish? Once you've got a defined goal in place (preferably something more than "good sound"), you can get to work selecting components.
Of the components you can purchase, the speaker requires the most thought and effort in selecting: the speaker combined with the room determine the sonic signature of your system, and in that respect, it is more than just a tool. Still, from a practical standpoint, you need a speaker that can play loudly enough in your room while maintaining composure, so you wouldn't want to pick a small speaker to try and fill a huge room. From there, things get easier: the characteristics of the speaker (namely sensitivity and impedance) combined with your volume requirements determine what you need in terms of amplification. The speaker combined with the length of the wiring run determines what you need in terms of speaker wire. The CD/DVD/Blu Ray player simply has the job of reading the disc and transferring the contents to your processor/receiver.
Approaching things from this standpoint can be a big money saver: if you're not interested in high volumes, there's usually not much need for a high power amplifier; if you're running an eight foot run from your amplifier to your speakers, odds are good that you don't need 10 gauge or thicker cabling. Pick the wrong tool for the wrong job, and you'll either have spent more than you needed to, or you'll end up unsatisfied and probably buying again. Buy the right tool for the right job, and you'll only have to buy once. Happy listening!