Yeah, I hope we haven't sidetracked this thread too badly, but it does feel like we are kind on still on topic. 
I hope my rambling response doesn't annoy anyone, and if it does I apologize.
And don't worry about offending me, you certainly didn't. I think the hype about SS vs tube is a bit overblown and was just trying to point out that power is really separate from that. And it seems that's understood.
My *guess* is that the difference you heard between the two 50W amps was either due to the overall build quality of the 2 amps or how the output circuitry interacted with the speakers. It sounds like you're also an engineer so you can imagine what a circuit diagram would look like if you laid one out for the entire signal chain of our gear - it would go on for miles! There's just SO many variables and interactions that I believe it's really impossible to predict what the final sound would be. So maybe a different pair of 50W SS and tube amps would feel completely different (where the SS would sound more powerful). That's honestly one of the most frustrating things about stereo to me - how I can't analyze or predict or read specs to *know* how making a change will affect things. It really comes down to "make the change and see if you prefer it."
I really don't know how accurate the gauges are, but it's very good equipment and I can't think of a reason for them to underreport the power used, so I trust the measurements are basically correct. Certainly within an order of magnitude.
I think all amps require fairly substantial headroom in their power supplies to sound good. I think considering things from an energy point of view (instead of just power) is helpful and that's where the power supply comes into play. It's really the energy storage portion of an amp and will determine whether the output circuit can supply the required power for the time required. If it doesn't have much energy storage it will initially drive the output circuit well, but then collapse as the energy stored depletes. Again, that's true of SS or tube though - it comes down to the design of the piece. I think the power ratings relate more to ability of the circuit (particularly the output circuitry) to handle the strain of driving the power for a sustained time. Good equipment is usually conservatively rated so it will be able to drive much more than it's rated power for short periods of time but eventually the drive circuitry will start to overheat and distort - or fail - if driven far above spec for too long. Maybe this is an area where SS has an advantage because the transistors are bolted to heat sinks, so it can more easily get rid of the excess heat, but I might be wrong.
I have never looked for a flea-powered SS amp, and I suspect there aren't many. It's so cheap and easy to add power that I don't think anyone does it. It might actually be hard to find transistors that can ONLY output 1-2W. Just looked at a distributor's site and 1.5W transistors are tiny - they're available in SOT23 packages! It's too late to research this now, but I suspect that if I looked for the smallest audio-grade transistors they would just naturally be rated at 20W or more. And designing a power supply capable of constantly delivering 10W or more of clean power isn't a challenge either I believe. I'm a digital guy, mainly with embedded systems experience, so designing audio and analog isn't my specialty, so I am just going off general experience, but I feel I am on solid ground. The lowest power SS amps I can think of are Pass labs class-A amps and they are rated at 30W and they are very highly respected.
Writing this, I wonder why the flea powered tube amps are designed for only 1-2W? I suspect that the tubes that produce the sound quality that the designer is aiming for can only handle these low power outputs, right? I just don't know tube design enough to be sure of that, but I suspect there must be something about the design or selection of tubes available now that if the tubes drive beyond that level the sound characteristics of the output circuitry aren't what the designer or owner wants. Does anyone know if that's right or if it's something else entirely?
The good news is that it seems that moderate volume listening doesn't really require more than a watt or 2 so these smaller amps are able to do that well, regardless of what their drive circuit technology is. And like so many things, quality is more important than quantity. I have really enjoyed "chatting" with you about this and would happily continue doing so, but I think if we do, we should create a new thread.
-Paul
