Given you are testing with KEF R3 speakers, and the impedance of the speakers is (as Measured by Amir) 8ohm nominal with a drop to around 3 ohm at the woofer crossover...
The requirements on the amplifier performance envelope are by no means difficult... a little bit of grunt is needed due to the 3.2ohm minimum - which will require a bit of current - but it's not like it is dropping down below 2 ohm.
There is nothing there that should put any of the amps into the difficult zone, where nasties are exposed - they should all behave like "wires with gain".
It is worthy of note, that the most difficult part of driving these speakers is in the bass area - and that is where you are noticing minor differences
Thanks for the analysis - I don't know how to interpret the MTF graph myself. I'm using R3 to compare amps because they are my new shiny speakers, but I also have DBR62 and they are a harder load I think (lower sensitivity and Amir's
review mentions beefy amp needed). Would listening on them help reveal differences between amps better?
I'd expect lower powered amps will lose dynamics at the hard frequency range at lower volume compared to the more powerful amp. Definitely want to hear an amp towards its limit as part of the education and comparison, the AIYIMA 07 (TPA3255) is the one I'll look to max out eventually for such test, don't think I have any speakers around that would get Onkyo AVR, Purifi or Hypex amps to struggle to drive.
Although you described your comparisons between the other amps - you made no description comparing to the Onkyo?
Was there no noticeable difference?
Currently listening to Onkyo vs Purifi on R3 - first proper volume-matched comparison I do, assuming these amps will be the most different from the set. No differences heard yet, but continuing to listen and not finished with the comparison.
After done with the Onkyo, l'll listen to Hypex and TPA3255 vs Purifi. Planning to take my time with it, it's obviously very hard to hear differences and might take me awhile to improve my listening skills.
Curious, have you trained at all for listening or have you tried Amir's listening skills video or ?
No training. Seen Amir' video, understand proper procedures for blind testing and know basic statistics to evaluate, but I'm not there yet in the process.
I'm aware of Harman's old "How to listen" app, but not sure if it's relevant to amplifier comparisons as it teaches recognizing mostly tonality differences.
I'd appreciate pointers to listener training materials if anyone knows any!
Concentrating on the recording is a more useful thing than concentrating on an amp in my experiences over the years. I find amp differences insignificant in general among my various amps, and going thru more than my informal testing for preference just isn't all that interesting (and can be difficult to do).
I arrived to the same mindset myself too - not listening to "amps", but the details of the recording and overall experience with it. As for amp differences, I want to figure it out this once, be done with comparing amps for life so i can focus only on the music not gear going forward. After doing the same comparison exercise with DACs too though