To me and my $.02 it's all about the holy grail....synergy....the ability for things to work together and for features and strengths of each part of the signal path to actually benefit from the piece that goes before it, and after. It's a simultaneous equation, best case, but to me the two biggest culprits in synergy-making are:
1) the room/speaker interaction
2) the speaker/amp matching.
Simply put, depending on the size, layout and acoustic potential of the room (let alone WAF), you have a certain set of speakers to choose from, given your ears and likes/dislikes. Start there. Then, and only then can you make an informed amp decision. Why? Cuz if the three sets of speakers that are on your short list are all 83 db efficient you can rule out most tubes, all SET amps and most low power ss's. You need brute force, with a touch of kindness. And that's only the ones you can't use!! Even knowing that you'll need power, some amps just don't like some speakers, regardless of impedance matching or any other Julian Hirsch-like math you want to do . We read about it in these forums every day. To me it's the most mysterious and black art portion of the search (and not necessarily the most fun)...it's like when I walk my dogs down the street; they yelp and whine for the weirdest pals across the street, and growl and go spaz for what look to be kindred spirits.
These are my $.02. YMMV. But they've not gone wrong for me so far. To me the final synergy ingredient is the preamp/source match, and those are usually done to taste. Digital sources can be fun to evaluate, but the signal path choices (hard disk, universal player, cd only, cd-r reripped with magic, media servers, wireless options, Squuezebox vs Roku vs Olive vs iMod) change every day. The only real stalwart and consistent choice in sources: a damn good table with a proven arm/cartridge match.
All in all, it's a journey that has no end, but has wonderful offroads and scenic overlooks. I just left one and decided to travel on to find a better view. Wish me luck. I hope to find new persectives, and maybe make new friends.