Can a great system make a mediocre recording sound good?

I find it to be opposite. My really good system makes bad recordings almost unlistenable, It will make average recordings some better some average.

Our perspective are not exactly the same, but it is related also to the genre of music we listen to...

Most of my bad recordings in jazz or classical are more listenable in my system even if they stay bad...

But pop or rock may be exception.... The jimi Hendrix two albums i refer above are unlistenable because of compression...the mix in studio is horrible work...I hate too much mixed in studio music... I prefer natural instruments in natural acoustic room with minimal mix ... 

There's a reason why the epithet "forgiving" is quite high up there in the audiophile vocabulary.

In a poor recording a system can't reproduce something that is not there. An "accurate" system will play the good and the bad. It is not designed to fix the bad just reproduce what is in the recording.

For me it depends on what makes a mediocre recording mediocre, by the way, I'd judge a large proportion of recordings as mediocre. I've found mediocre recordings that formerly had timbre, sound staging and/or were less resolving have become much more listenable. A highly resolving system with more natural timbre or tonality will uncover information previously unheard, and presents recordings in a more forgiving manner. Recordings with these defects become more involving.

Quashed micro dynamics is one defect that's been heightened by a more resolving system. I find far too many digitally mastered recordings to suffer this malady, I can only take these recording in small doses, consecutive plays of these recordings causes me to lose interest, have to return to known high quality recordings to return to involving listening session.

Poor recordings remain poor, no help can be found for these.

Not this week.