Suggestions on improvement

For that amount of $$$ I think you’re relegated to cables or something like isolation tweaks. Here are some very good speaker cables that could potentially provide a meaningful upgrade, and if they don’t you can turn around and sell them for little/no loss so pretty low risk. I’ve recommended them to several people here and they’ve worked out very well with the obvious caveat that cables are always a bit of a crapshoot.

https://www.usaudiomart.com/details/650117484-acoustic-zen-satori-shotgun-biwire-speaker-cable-8-foot-pair/

You didn’t mention what interconnects you’re using between your CDP and amp, but that would also be a potential area of meaningful benefit for not all that much money. Hope this helps.

That Marantz cd player can be improved upon greatly. I wouldn’t touch anything else until you get the source game up.
What is your budget for the improvements? I would recommend a good dac to use with the marantz as a transport. Or ditch the marantz altogether - find a used Aufiolab cd transport and pair it with a nice dac. You will be amazed by the upgrade in sound quality. 

If at age 78 you're still getting your beard buttered, you have no real complaints. As for your system, acoustical treatments aren't necessarily ugly. Wite panels on a white ceiling are practically invisible and make a big improvement on the largest flat acoustically reflective surface in your environment. 6 - 2X4 ft panels would add 48Ft2 of broad band absorption. We added about that much to the ceiling in our slope ceiling living room. Not only are they not noticed visually, my wife definitely noticed how much more 'intimate' (her words) the  space feels with its liveliness tamed a bit.  She's a believer in acoustical treatments now.

OP, as a fellow subject to aged hearing that also began with loud tools and loud...louder likely music as baggage...

Do you wear aids?

-or-

Would you accept an equalizer that had room correction abilities?

-or-

Both....like me?

...the ’rest of me’ is my own problem....*L* ;)

If traps won't fly, I suspect panels overhead won't get to either.....

An eq up to the task, 'reasonable' cables to knit it in, and a calibrated mic as it's 'ears'.....$1K ought to do it, shopping 'hard' for the sweet stuff if you must...😏

...and you can always 'tweak to taste'....;)

Mho.....If you're 'buttering your beard'.....either wasting it or not performing 'proper'....

My mustache?  Yes, Certainly..need not ask.

My beard?

Go to go in that latitude.....a visit to the Hills, perhaps.....

Anywhere Else?

....I trust y'all have That figured out by now.....🙄

......I don't drop mics...