I've narrowed it down...

With all due respect to some of the other posters, I suggest buying amps for speakers, not speakers for amps. I suggest that one find the speakers one likes, and then buy the appropriate amplification.

I suggest auditioning speakers WITH proposed amps.

Buying speakers for amps OR amps for speakers is the short way to madness.
Buying / auditioning together, especially for people just learning, is best done in a shop with some experienced guidance.
Online? Well, that's much more of a risk, IMO. Unless, of course, some background exists to ease the choice / reduce risk. Others have the 'buy it used and test it' philosophy, thinking they can sell whatever for pretty much what they paid for it.
The online approach is, to me, anyway, for the more experienced or those with deeper pockets.

Un, with much more experience can target into a class or perhaps even a brand of amp which has very high probability of satisfaction.

Overall, I'd say to buy the source first. That'll make run of mill stuff sound better and perhaps even survive a few upgrade cycles.

I agree completely with unsound, as far as picking a tube
Amp? Once you find the speaker that
You like, find the impedance chart for that
Speaker and look specifically at phase angles.
The dips or capacitive angles are what give tube
Amps a hard time

Speaker then amp or amp then speaker,'either' method works out . In the end they both have to match, chicken or the egg.I based my system on a move to a SET amplifier and it worked out fabulously, you just have to have a well thought out plan.
Regards,

Unsound, what you say is normally correct, but if a person wishes to go the tube route and has incompatible speakers for tubes shouldn't fellow members here tell the potential tube buyer that information? Then he can go find the speakers that he likes that are synergistic with tubes; and by-the-way, many people know for example that they prefer tubes to SS after hearing tubes, but might not understand that their current speakers are not a match made in heaven, so, the reverse of your normally correct theory is reversed. As the old saying goes, " more than one way to skin a cat."

I knew that I wanted SET 300B sound, loved the Cary house sound, bought the amp and went out and found the right speakers to match up with them, not more difficult to do than the other way around.