What to judiciously invest in next to improve SQ?

[zambie]

Pim’s advice is sound.

Speaker isolation (de-coupling) was also useful in my space - much more so than coupling.

And playing with DSP and room measurement is useful just because you can see what small EQ changes (in the right places) do - sometimes it’s quite profound. And if you get bored you can change it some more and listen to new details in your albums.

If I could go back in time, id buy a umik-1 and learn a bit about acoustics/rooms before buying any kit/accessories. I left it far too late and it’s really the only way to tweak your setup, or not the only but vital IMO. Otherwise you just don’t know what deficiencies you’re trying to fix (and unless you’re incredibly lucky, you’ll have deficiencies in an average room that no upgrade will fix) and trial and error without any measurements is needle in haystack stuff.

Lots of sound advice ... .. both you and Wdw have given some good insight on the isolation front. Will research a lot more about room acoustics - it's an interesting topic for sure.