This first: Know yourself.
If you know what you really want (from life or from your sound system), you will be better equipped to make intelligent choices about the best way to accomplish it. And unless you are infallible, this whole process will still be a trial-and-error journey; in addition, what you want may well change as you change.
Thus far in your audio journey, haven't you learned a great deal about what you do and do not want from your sound system?
Getting to the question at hand, I don't think you should choose the amplifier with great care and then throw just any speaker on it. Nor do I think you should do the reverse, unless you're Dave Wilson giving a demo! And even then, I suspect he took the time to find a cheap amplifier that still sounded pretty darn good on his speakers.
In my opinion the question to ask oneself is, "What am I really trying to do with this sound system?" Once that question has been answered, the next one is pretty obvious: "What's the best way to accomplish what I want?"
Here's my generic answer to the first question: "I'm trying to recreate as closely as possible the aural perception of a live performance on music that I listen to a lot within my budget and without creating a sore spot in my marriage."
Now to the best of my knowledge there is no well-established consensus on exactly what the minimum requirements are to recreate the perception of a live performance - so there's still lots of room for individual interpretation as to the best way of accomplishing that part. In some cases the speaker/amplifier matchup is not critical (as Dave Wilson has demonstrated), and in some cases it is very critical (see Atma-Sphere's post above).
I think that in most cases the speaker's characteristics have the most influence on the final sound of the system. Sometimes this will significantly narrow down the amplifier choices, and sometimes not.
[As a side note, an amplifier's input has variations in the domains of time and magnitude (voltage), as does its output. A speaker's input varies in time and magnitude, but its output varies in those two domains plus three dimensional space. So I claim that at least in theory speakers have more opportunity to screw things up - which they often take full advantage of!]
Now some people place a very high priority on the beneficial characteristics of particular amplifier types - SET and OTL come to mind. For these people, amplifier type (if not specific amplifier choice) will come first. Once that choice is made, the range of speakers to choose from will naturally narrow down considerably.
Personally, there are certain types of amplification I would like to use, and certain types of speakers I would like to use, because in my experience these do a good job of taking me down the road towards what I want.
Duke
