Distortion

The worst amp I ever owned had .001 THD. 

So the OP is implying that expensive amps with low distortion sound bad???

First of all, who says that audiophiles look for brands with the lowest distortion specs?  I have never heard anyone with an expensive system mention the distortion percentages of the equipment and some of the brands you mention have higher distortion ratings than much less expensive products.  But as to the second part of your question, when you say "distorted" music, I assume you mean electric guitar and such, where the players deliberately add what is commonly called "distortion"?
In simplest terms, the goal of home audio is to reproduce what is on the recording.  If the musician chose to produce a distorted tone, the system should reproduce it as it was recorded. If the home audio system has audible distortion, it will not reproduce the recorded sound accurately.  BTW, I think you and many others consider distortion to be limited to  noise or some objectionable sound.  It may be, but in fact any alteration of the original sound is distortion.  If you boost the bass in a way more pleasing to your ears, you are distorting the original sound. 

There is virtually no correlation between % THD and what passes for "good sound". Simple listening tests show this very clearly.

Some folks have a real hard time with this and will do their level headed best to convince themselves, and everybody else, that the lower the THD the better the sound. Most audiophiles do know better; these folks are actually a small minority.

Over the years I have noticed a strong correlation between folks who believe low THD means good sound, and those who cannot hear the differences in cables, component isolation, power filtering etc. The logical conclusion is that they have hearing deficiencies and have no option but to rely on measurements when choosing components. 

   "professional audiophile"

Those 2 words put together just looks silly.

Carry on.

It is highly unlikely you would be able to any harmonic distortion less than 0.5%. Just make sure not to clip the amplifier!

Distortion is not tolerated in high end audio. But in live music its much more accepted.
In order for you to listen to a stereo system for a long period of time (2 hrs or so) at a loud volume level your ears cannot be hammered by distortion!

Thats it!
Matt M

+1 pauly
I like how my ears/brain are connected & respect engineers who don't disregard theirs when designing high end equipment.