Since you started with non-electrical components tweaks keepers, may not be cost effective in some......;
1. Auralex's acoustic panels & Realtrap's Minitrap are on top of my list. They have "transformed" my smallish listening room into a concert hall.
2. Roomlens Helmholtz resonator units for damping out unwanted room resonances.
3. Symposium acoustic products. I 'm using their platforms under all my equipment except for the speakers & they are brillant in bringing focus & clarity to the musical experience. I 'm using their Rollerblock Series 2 Double Stack with the top Grade 3 Superball under my CDP as well, another winner.
4. Herbie's Audio Lab products; CD Mats, IC Dampers & Hal-O damping instruments for vacuum tubes.
4. DIY Cable lifters made out of wooden disposable chopsticks.
Cheers..........
