Can a great system make a mediocre recording sound good?

yes I totally agree garbage in garbage out, I have a $60,000 system which includes a Sim audio p8, Sim audio w8, esoteric P10 transport, Wyred4sound 10th anniversary dac, monarchy audio up sampler, and for the speakers monitor audio platinum 200 Gen 2, a friend of mine brought over some of his CDs that were not so well recorded and boy could you tell the difference from other CDs that were well recorded it wasn't even close.

I've found that most 'poor' recordings only sound poor because the system/room I was hearing them in was not good enough to translate the acoustics of the space the recording was made in. There are much fewer poor recordings than we generally believe exist; and more poor systems/rooms that make us believe the recording was poor. The best sound/room systems accurately allow the decay and reverberation of the recordings to complete what we understand as the soundstage, such that what once sounded like a poor recording was merely an inaccurate or incomplete playback of the uniquely altered sound of instruments and music in the specific venue of the original recording. 

In friendship, kevin.

What I have found is exemplified by my run in with Jimi Hendrix ‘Are you experienced?’.  When I play it on the system I have today (for nostalgia sake) it’s almost unlistenable … harsh, bright, compressed etc … though the music still good.  It just never sounds as good as it did on my parents cheap console system 40 years ago even when my hearing was better.  

The simple truth is a very good system is probably very revealing as well. That said a lousy recording will be lousy !! You can waste your time with room treatment and or the dials only to end up with lousy !! Play a noted well mastered Selection then without touching anything throw on some old Rolling Stones. Their not in the room with you their in that Sony Walkman lol. Pick and choose new and old it’s out there.., turn it up and smile when you find it.

All systems are imperfect.  That is they cannot perfectly reproduce the signal fed into them.  Therefore the sound that comes out will be judged either 'better' or 'worse' at reproducing that signal.  The systems that are 'better' will be improving the sound of the (poor) recording.

Therefore a system could be designed that would process poor recordings to sound like good ones.  But the changes made would render the performance different from the original recording.