Have I Hit The Point Of Diminishing Returns?

Yes, you past the point of diminishing returns as soon as you go past your first boombox. The laws of diminishing returns hit early and hard, just as in any other hobby. A $10,000 watch is not 1000 times better than a $10 watch. Same goes for audio gear.

You have stated twice that you are very happy with the sound of your system. My advice would be to buy more music and just enjoy it. Don't let others spend your money for you, unless you are just dying to throw money around. If you are happy, there is no need to seek out unhappiness.

Cheers,
John

John - Thanks for that. I was just curious as to how much
better it could get versus cost. Perhaps I've got
"upgradeitis." However, to pay a significant amount
for a de minimis improvement or difference in sound, makes
little sense to me. It just may be time to get off the roller
coaster and focus on the music rather than the gear; being a
gear geek, that's not so easy.

We all have - long ago.

Here's a bug in the ear suggestion. Take it for what it's worth to you.

Grace Design M920 w/remote --- $2300
Neumann KH310 active monitors - $4450
Balanced cables of choice --- $ 500
------------------------------------
TOTAL $7250

You can use your tuner as before and use your CD as a transport. Mission accomplished. You will never look back.

+1 Doug Schroeder. Best of Luck

My listening room is nearly identical to yours and I recently tried something that made me sit up and say whoa.
I set my system in a diagonal configuration after reading this. The increase in soundstage depth alone was worth the effort. But honestly, as far as I can tell there were improvements in every sonic attribute of the system. And yes, my room has significant treatment going on.
If your system is movable you really should give it a try. I'm usually not much of a fanatic but I am a convert and am spreading the word.