Ok this will be a good thread.

Screw it, get a Bose Wave Radio and let the mind take over and enjoy the music. Maybe that's the only way only one component can get us anywhere near where we want to be.

Wow, there are a lot of perspectives here and it seems most are correct given their underlying assumptions. Twl, if the rest of the system is decent, I believe the front end makes a huge difference. If any one part is insanely bad (per your point KF), surely nothing else matters but replacing that part. Great speakers can make a very good system sound better (and, by the way, speakers are a good place to start if you hate buying and selling heavy and bulky things and/or if you are aiming for a specific "sound" that is characterized by a specific speaker). For me, the most important part is the one I want to upgrade next. In other words, so much depends on the system already in place. To paraphrase, if the a**hole works and the brain works and the heart is in trouble, the heart is the most important.

WOW. I just got back from CES in Las Vegas. I had a National Sales Meeting, that is why I got home on Wednesday. The show was over on Sunday. I knew this was a good thread. 91 posts.
Anyway after taking the time to read the replies I think JAX2 is right. Also he actually read my initial post and saw that I asked what was the most important part, and what had the most impact on the system.
Steve

1) Room. Speaker placement within the room and room treatment will have the biggest impact on sonics.
2) Amp-speaker interface. Matching the right amp with the right speaker is more important than just buying a great amp and a great speaker.
3) Speaker. Spend alot of your money here.
4) Front end. This used to be higher up on the list but I believe digital has plateaued in terms of improvements.
5) Don't forget power conditioning. It makes a big difference.

I do not draw a distinction between the most important component and the component that makes the most impact on system sound. To me they are one in the same.

KF

The initial question or questions are somewhat ambiguous for me. Not because the question marks are missing, but you can take the first two sentences two ways.
1."What....is most important..."
2. "OR what has the biggest impact...."
"OR" can mean "instead of" or "more specifically".
3.Further down seems to clarify the previous questions, "....JUST what do you feel is most important.(?)" indicates the question may be looking for a single component.
4."...but keep it to one part..." seems unambiguous.

Sometimes the intended meaning of a post is misunderstood for any number of reasons in this type of forum and it's often because the post is not read thoroughly. Even that does not guarantee you will understand the intent of the original post.