Yes it was a joke but a joke with ground in what a user expect when listening.
We need to clarify what this fr linearity it is. Maybe the readers expect that a flat FR will give them an excellent sound with sufficient bass and nice highs and clear full body mids...but this is not the case. Because the second component in their system are the speakers. A flat response curve in an amp will give default an ugly sound...with depleted bass and to much energy in highs and thinned mids. Why? Because all bass drivers are less efficient and will need always more energy to move that mass of air, and the highs will require much less energy. Also the FR graph need to be done under load scenarios...volts and amperes. The crossovers in speakers will always attenuate the mids and highs and will shape a little the bass.
No 2 speakers will be the same because different crossovers and different efficiency drivers. All low cost and medium cost speakers maybe until 5000$ approx mark will lack in bass...sometimes in mids and other times with cheesy highs. Coupled with this type of this class d amp always will sound harsh shooting and devoid of low frequencies...without an dsp in the chain to favor low freq and equalize the sound. pa5 compared to da9 sounded more thin because some low mids lacking energy in favor of higher mids and higs.
I think you are confusing operations. The amplifier is amplifying a sine wave agnostically in terms of FR and without distortion. That’s it. It isn’t a music production device. A good speaker design will take that signal and produce a flat FR from 20HZ to 20kHZ with minimal distortion. You can then treat your listening space and use EQ to create the FR you personally enjoy. To ask the amp or the speakers to do it is essentially building fixed filters into your audio reproduction chain. Which is an inefficient way to make equipment and one reason for unnecessarily high costs.
Everything you are claiming (without evidence) are the flaws with reproduction systems. You don't need to know load to know how an amplifier will perform. Voltage by frequency tells you that. Load is speaker dependent, but the designer should take driver load into consideration. If the crossover in your speakers is poorly designed so you get too much bass or too little mids
or whatever, then that is an issue with the speaker, not the amp.
Transparent DAC. Transparent AMP. Transparent speakers. Transparent room. That is how you reproduce the recording. We are not making music with our stereos. We are listening to it. If you don’t like the recording because it is too bright, too dark, too clinical, just Eq to taste and/or drop an Audio Unit to season it to taste.
By the way my $300 for the pair speakers produce excellent bright base, with mids that are luxurious and salty, and peaks that massage my brain. Excellence and cost are only loosely related, especially in a data free context.
) It is transparent mostly where should not be 
