Most impactful for playing soft

Speaking plainly, I consider what you have just observed to be the difference between your system and the next level up (maybe 2 levels if you take small steps).  

To get to where you want to be I'd replace every component you have named.  

Jerry

During my journey I've found the better the system the less need to want to play it loud. (85-95 db) and the quieter the music seems because the 'space' is more accurately presented. 

After getting my system components in place I noticed power cables made a difference in the clarity and presentation of low frequencies.  It was very unexpected to me.

Not so fast…human hearing requires a loudness curve for a reason…

How loud ( spl ) is the spouse acceptable level ?

Integrate a nice subwoofer to fill out the lower registers. 

I’d look at properly applying DSP functionality in products like Roon or miniDSP to help adjust for room acoustics. Adjusting for room acoustics addresses the root cause and allows all the music to come through cleaner and better at all volumes.