What is stopping the ultimate?

Clueless (who isn't) smacks the nail right on the head. The electrical interaction between the amplifier and the speaker is wayyyy complex and cannot be deduced from reading the spec sheets of both. You have to do it with your ears. That's why amps with very similar measured characteristics sound so strikingly different when connected to the same speakers and why speakers sound so very different when connected to the same amp.

I wouldn't say that at some point in the future these matters couldn't be measured and quantified but at this point we've only got one way to do it....with the ears.

Very well put Bishopwill. Good common sense point.

Further on Bishop's & Clueless' points on amp-speakers interaction: one of the reasons high nominal power amps have a market IMO, is the current reserve the manufacturer has to include in order to achieve specs such as (fortuitous example) 250W class A, measured @ 1kHz signal/8 OHM constant resistance. This power capability allows these machines to perform under normal listening conditions at reasonable db levels and deal with the varying speaker load (+ the crap from the c/overs).

Similarly, with tubes: allegedly, many of the power supplies provided for an advertsied output of 2-digit watts the power supplies are overkill -- according to traditional EE theory. This comes from hearsay, I'm not an EE...

On the other hand, for me, the original question still stands -- bar active speakers and our zero control over recording and s/w production phases: where's the ultimate?

Lack of standards throughout the chain, from microphones to speakers. Two channel sound. Overproduced recordings. Producers and engineers by law should only be alloweed three microphones when they record. Too much editing of recordings. Too many variables in assembling systems: manufacturers should offer more all inclusive systems with everything hard wired from a to z (would audiophiles buy them: buying, assembling, disassembling and selling is the heart of the hobby, no?). At least more active speaker systems to avoid mismatches. And last but not least, improved speaker systems, not that good ones now are bad, simply that they are the hardest part of the system to design and build to the highest level.

If you ask me, the recording quality. Some of my favorite CDs sound like crap unfortunately. My Mcintosh setup does the best job of all the ones I have tried to prevent a constant hiss from coming through but the recording still sucks. Perhaps when the cat fight of SACD and DVDA is over, we can settle on spending time and money on IMPROVING a common standard (as was mentioned) that should include recording company equipment quality as well.

As far as the steady current thread above between speaker and amp, it IS totally quantifiable and I have calculated it for my setup but let me tell you, it is supremely complicated and is dependant on all parts of the system. You change one piece and everything has to be done over again. Flux linkages from the cables, output circuits, and speaker coils are all intertwined and consequenly affect both voltage and current continously and are the main reason for differences in sound and fluctuations in output. Mcintosh realized this years ago and with the inductor-coupled output (autoformers) they use on solid state amps, they can reduce the effect by dominating it with a known variable - a fantastic concept. Electromagnetics are very complicated and so you might as well forget about calculating, since even that is an estimate at best, and just listen for yourself since the end result is what your ears like.