I would say the amp/speaker match is the most critical, get that wrong it doesn't matter. Get that right and most decent preamps and sources will be ok, and only better as you upgrade, but nothing will ruin things faster than an amp and speaker that do play well toghether IMHO.
Which has greatest influence?
I have recently upgraded my amp but got to wondering which really has the greatest affect on the quality of sound --the preamp or the amp? Or is there a difinitive answer to that question" I have heard it said that your s ystem is only as good as youre weakest componet. Is this always true?