Let me end the Premp/Amplifier sound debate ...

First off, +1 on what @atmasphere said.

Secondly, the folks at ASR display myopic hubris. Many folks there literally would take a $400 Topping amplifier over an Atmasphere, Pass Labs, D’Agostino, etc. amp based on measurements alone--without even test driving them.

Go try posting on ASR and asking them how things sound. They can be so evangelical with this framework. Many, not all, of them do not talk about how things sound. The ASR purists believe if it tests better it must be better. End of story.

While testing has its place and can be of meaningful value, it’s not everything.

Also, I’m not entirely sure ASR is truly an objective service to the audiophile community. ASR may be monetizing a testing operation, and some folks say that ASR is tied to certain brands. I believe there’s a thread at Super Best Audio Friends or something where they have intel that Amir has a relationship with Topping or SMSL or one of those brands.

See Audio Science Review, Review 

Voltage from a tube amplifier OPT will vary considerably depending on the speaker impedance at the test frequency.

@ieales This statement is incorrect. This amp uses about 15 dB of feedback, allowing it to behave as a voltage source with most speakers. The variance at the output transformer is thus minimized. If it was zero feedback then it would behave as you describe.

Most everything has a signature sound characteristic. Every resistor and capacitor has their own sound.  That also goes for transformers and chokes.  Even the chassis material has a sound. 

While this is correct, it is incorrect to say that in all cases the 'sound' of the various parts actually influences the output. If the amplifier has enough Gain Bandwidth Product to support a large amount of feedback (+35dB) over the entire audio band then the various parts 'sound' will go away. Most amplifier designs cannot meet this criteria and so the parts influence the sound as you describe.

I have very limited experience compared to a lot of people here but I've heard all three in my system and one was the clear winner.

I would agree pre amp is the most important thing which has had the greatest effect on my system.

It seems to me, that the bottom line here is that all people hear differently. Some people have very acute hearing; other people don't. Those people who have very acute hearing maybe will hear a differences between various amplifiers or preamplifiers and those who don't have such acute hearing will not.  Those who don't hear a difference will think that there are no differences, while those who have better hearing your differences. The real issue is how you feel about the sound of your equipment. If you can't hear a difference there's no reason to spend more. I know I for one get jazzed up about some component based on reviews that call it the best thing since sliced bread and I am compelled to want to buy that piece of equipment. When I put it in my system I find that it might have a better sound in some respects but no means is it "a night and day oh my God I have a new system type" difference like the reviewed portrayed.  I think that the real interesting point made by the OP in this case is the diminishing marginal utility of equipment. Is there a $10,000 difference between a $10,000 preamp and a $20,000 one, or is it just audible. If it's just "audible" then, one must decide whether that "audible" difference is worth another $10K.  That is a personal choice and there is really no right or wrong.

Eric, great post and worthy of discussion.

By the way Todd, very nice setup. I’m sure you enjoy many listening sessions. By the way I had the Yamaha ZX-9 many years ago and gave it to my son. It’s a fine-sounding receiver.

On Amir and ASR, I respect what he is trying to do. Amir’s opinions are worth listening to and he has some very good points, but many ASR forum members are just annoying. Speaking from my personal experience, I believe the measurements we use as standard do not tell the whole story. Not at all.

In my humble opinion, I cannot understand how any audiophiles obsessively build their sound systems over the years and still believe that all amplifiers, when level matched, essentially sound the same. I find that contention wildly wrong. Without going deep into how different topologies sound different (to me, they most assuredly do), each amplifiers model is capable in different ways, with strengths and weaknesses. Some are extremely fast and ‘airy’ , whereas others are more rich, and seductive. Some throw massive enveloping soundstages and present as a complete sound-picture you look on from the outside, while others focus more on immediacy and ‘I am here-ness’. Some are more laid back with a slightly recessed perspective, while others are very forward.

My believe is, that as technology advances, the higher-end products are becoming more similar in sound, being better able to approach the ‘absolute sound’.

For example, a Devialet Expert Pro sounds different than a Parasound Halo, or a NuForce, or Audio Research Classic 150 mono-blocks, or a bridged pair of Mark Levinson 27.5 and so on and so forth.

Pre-amps and Cables; same thing.