Diminishing hearing ability?

You can have your ears cleaned professionally.

You can't do anything about bad source material. If it's not recorded and copied well you are SOL.

You might be surprised and disappointed were you to listen to your 5k system today.

I suspect it's probably not your hearing at all that's to blame. I suspect it all actually stems from the basic premise that it just ain't that easy to assemble a system that knocks your socks off. Most systems I've heard and that's a lot are kind of blah, to be brutally blunt about it. If it were easy everyone could do it.

90+ year old conductors can conduct because the brain can fill in gaps from memory.

I agree with Tostad, I wanted big Infinities back in the day , heard some in recent years and wouldn't want them for free now .

How is your health? Does ANYTHING knock your socks off these days?
Try hitting the treadmill 3-4 times a week for six months. It works for me!

What is a great listening experience? Is it the sound? The music? A combination of both I expect. Audiophiles, when we obsess about the sound of our rigs, will play those familiar cuts, over and over, that we use for intellectual analysis of the performance characteristics of our systems. But I suspect a great listening experience to be more connected to our emotional response to the music. Rather than obsessing over the nature of the cymbals, the resonance of the bass, how about connecting to the artistic performance? - of new or unfamiliar music? Certainly, I, along with others I might assume, are guilty of the analysis posture - which might include assessing our diminishing hearing. But, on occasion, to relax and be open to music itself, might and can provide the possibility of the great listening experience. IMHO