Which has greatest influence?

The end of Bokfudo's post nailed it. During my long since past audio career - it constantly amazed me how often I'd sell some at least decent speakers to a guy and then find out they'd been set up in some absolutely bizarre configuration.I am also completely convinced that the classic British approach to a HiFi system is most likely to lead to a great result : Listen to and then buy the best source you can possibly afford , try and get some electronics that will work with the speakers you like - but the speakers will probably continue to sound better and better as you improve the rest of your system.
For instance - many years ago at the Polk factory I briefly heard the smallest and cheapest speaker those folks made drivin by a system that included a pair of Threshold Class A Monoblocks - I had listened to those speakers both in my store and customers homes a lot and to be honest - wasn't terribly impressed- wow - given simply outrageous stuff pushin 'em - these were wonderful speakers.

Stonedeaf, Amen to that. Good upstream equipment can make relatively inexpensive speakers sound great.

Jacknorth, Before going out and spending money on new electronics you may want to try some Elrod cables, power and/or speaker. I installed them and it was like putting in a new upgraded component.

Only as good as your weakest link, hard to answer. Lets say you had nice equipment and speaker cables were the weak link, I think the system could still sound fine, you may not even be aware the speaker cables are the weak link. And so some things are more important than others, and yet they're all important. I'm trying!

Having to choose only between amp and preamp, I would have to choose amp. I say that because amps have to interface with loudspeakers, proper synergy is of utmost importance. Amps also just seem to give the most 'flavor' to a system, think about all the different tube configurations possible.

IMO, all system components should be matched as to level of performance. A $20,000 preamp will make little or no difference in the SQ of a $5000 system.

However, the speakers need to be driven by adequate amplification. That is more important than the preamp as far a SQ goes. Once that is achieved, then attention can be given to the preamp. Unlike an amp or the speakers, the preamp will determine the type of control one has over the system. Does one need tone EQ, remote control, phono input, computer input, headphone output, etc...?

Mike

Having just upgraded my amps and then my preamp, I found them to be roughly equally important, but each effected the system in profoundly different ways. For me it came down to what the amps do and what the preamp does not do. My new amps control my speakers much better than the old amps did. Bass is tighter, deeper and more focused. Dynamic range increased as well as improved soundstage size and definition. My new preamp gets out of the way much better than my old pre did. It is quieter and more neutral. Micro and macro details improved, timbre and transients improved. However, each upgrade made the listening experience more involving in roughly equal amounts. They are from the same manufacturer, so they work very well together. My system is built around my electronics. Its the only area I have really upgraded over the past six years.

Having said that, I have found the most critical component/relationship is the room-speaker interface. This is about scale, placement and taste. Then the speaker-amp/cable. And finally the amp-preamp. The front end is a completely different thing and can be thought of as its own system(especially analog). It can be of equal or better quality but is not as interdependent as those other components are and can be thought of independently from the rest of the system.

At least, this has been my experience having just upgraded my electronics.