The closest approach: what amplification?

It depends what sort of live event you are trying to reproduce.

I think it is possible to convincingly reproduce small scale acoustic music which has been well recorded.In this regard I find SETs or OTL are most rewarding.

Forget orchestral music or rock concerts however.At best you get a scale model of the real thing.
For orchestral music Bose 901s are probably the most convincing, seemingly regardless of amplification.Nothing else I have heard gives a realistic sense of soundstage width and venue acoustic.I hate to say it but Bose is right about this.Some sonic deception is required.

For me, it's zero-feedback, fully-balanced solid state matched with time
and phase aligned speakers. YMMV.

Unsound asked Bill about high output impedance... obviously I'm not Bill, but I'll take a shot.

If the amplifier has a very high output impedance (very low damping factor), to a certain extent the loudspeaker's impedance curve will "modulate" the amplifier's wattage output; that is, the amp will put out more wattage where the impedance curve is high and less where the impedance curve is low. This is the opposite of the behavior of an amplifier with a low output impedance, where the wattage goes up when the impedance goes down and vice versa.

Putting on my speaker designer hat, in my opinion the answer is to design speakers with as smooth an impedance curve as is practical. They will thus have virtually the same tonal balance with either type of amplifier, and one consequence is that such a speaker will allow a more apples-to-apples comparison of various amps. In practice it's usually not possible to avoid some impedance peaking in the bass region, and it might not even be desirable to do so; the increased wattage output of a high output impedance amp in the bass region can be leveraged to extend the bass deeper than it otherwise would have gone.

Having built such speakers for several years, and having had the opportunity to hear them on a fair number of amplifiers, in my opinion high quality OTL and high quality SET amps in general do sound the best. For most of the past few years my personal amps have been OTLs.

If the speakers were designed for contstant-voltage amps (most are) and have significant impedance peaks or dips above the bass region (most do), then I would still look for an amp with little or no global negative feedback.

All that being said, let me give an analogy from the world of amateur speaker building (my thing for twenty-something years). Many's the amateur speaker builder who sets out with high hopes intent on combining the best woofer with the best midrange and the best tweeter in the best enclosure using the best crossover. Almost never does the result live up to the promise of all these bests. The reason is, our enthusiastic amateur designer friend isn't taking a wholistic systems approach, based on the best outcome, and working backwards from there to assemble those components that will give this best outcome. Turning now to the question of what is the "best" amplifier, I would say look at the amplifier+speakers+room as a single system and go from there.

Duke
dealer/manufacturer

I would like to go back to Stanwal's point, which is an interesting one. Stanwal says that there are actual sound waves, but each of us HEARS different things. In my opinion, the personal experience of what we hear should be irrelevant to the discussion of what makes for a good audio system. The closer I get to capturing actual sound waves, the closer I get to the real experience. Then each of us can focus on different things in the listening experience. In other words, take Mahler fifth symphony. Out of the whole symphony there might be two minutes in which the deep vibrations of low frequencies are dominant. I know some people who love the symphony precisely for these two minutes. That's what they want to hear. Does it mean that for these people a good audio system is one that exacerbates low frequencies? I don't think so.

When I go to the symphony I am acutely aware that where I sit in the hall dramatically affects the experience. Under the balcony the bass is emphasized. Seats far away homogenize the sound. Up close the orchestra really does "image" with the violins on the left etc. At all points, however, the dynamics and the texture of the sound make all reproduced sound seem...well..simplified, flat and lacking in a host of important qualities. I think all of us agree on that. As Peter Walker said, like listening through a window. And a smudged window at that. So, what to do? For years I was in the "straight wire with gain" camp. Often that led to highly detailed sound that nonetheless still managed to get on my nerves! I have slowly migrated to the "are we having fun yet" group. A truly accurate map of the earth would have to be...well....the earth. So since we are of necessity in the simplifying and simulation business, I strive to recreate not the most mathematically complete model, but rather use a bit of trickery to recreate a bit of the emotional experience that draws me to music in the first place.