Speakers (1st always)
Room (2nd always)
Power amp
Somehow sources have never "done it" for me.
JLM, this is the order of improvement I always assumed to be the best guide, and still is what I advise others to follow. However, my experience tells me that circumstances can dictate what might have the greatest effects.
I used to have a sound room that was virtually square. Nothing, absolutely nothing, I tried could make that room sound right. When I moved to a new home with a good rectangular room, the difference was incredible. But was it an audiophile kind of improvement (i.e. diagnosing an issue, searching for a solution, buying the gear, etc.) or just eliminating a problem inherent in a room I had no way of changing? I count it as a dramatic, but kind of ass-backwards almost inadvertent change.
Before getting my 7BSST2s, I placed amps as number 3 as you do. However, as I explained in another post on this thread, my changed speakers did not show dramatic improvement until I changed my amps.
Moral? Despite the plain intent of my OP question, it may be that circumstances sometimes dictate that dramatic changes in performance come about with multiple changes in gear and other factors.
Dave