The Best Sounding Systems can Play Loudly with Low Distortion

I do not think the OP intends it, but the question uses the slippery phrase "best sounding". Imo, a false dichotomy is set up between lower and higher level playback and determination of "best sounding". I would expect a great deal of disagreement to follow. Nevertheless, I will attempt to answer the question based on the criterion of "low distortion". 

Superior sound quality is the mark of a truly great system, not the listening level.The limitations of a system is not found at lower listening levels but higher listening levels. 

Imo, the OP is correct; low levels do not as readily reveal distortion. An example; many audiophiles have concluded that compressed music is wretched, sounds distorted. Not true. In the vast majority of cases, their system is incapable of reproducing such music at higher levels. Perhaps 85-90% of audio systems represented on Audiogon would not handle such music well. Many of the systems I have set up for reviews have inherent limitations which would be revealed if I pushed them with compressed music. I include compressed music for that reason, to discover the outside limitations of the performance. 

Compressed music and much electronic music that sounds indistinct to many audiophiles is usually extremely detailed but in the part of the frequency spectrum in which it is played, typically LF, not many rigs can play it with high fidelity. So, no, I would not use low level listening as a basis for assessment of how precise a system or set of speakers. 

Another principle I espouse in my book is that a superior audio system must play all genres of music well at higher level, or it is not that great of a system. Again, this is not meant to demean anyone here, but to distinguish my criteria by which I assess systems. 

@douglas_schroeder 

Best response yet. Thanks. Yes, in hindsight, I could have phrased my assertion better, but was attempting to keep it succinct. 

My Carver and AR9's sound great at high or low volume

"Best for whom?" is always my question.  I actually think playing speakers loudly, when that's NOT how you listen to music is a terrible idea.

That's like needing a family van and racing it across the Mexican desert.  

Test/listen to speakers like you live. 

Leave the PA testing to live music performances. 

@helomech 

Who said anything about before 85db?  And if you look at my system, you’ll notice that there’s no way my amps are struggling or my speakers lack dynamic range.

You have totally lost me!

I would argue that if your ears give out before reaching 85dB averages at your listening position, you’ve either suffered significant hearing damage already, or you’re actually hearing your system struggling, either because the speakers lack dynamic range and/or the amplifier lacks headroom.