Best Tweaks.....

The following are the most effective lower cost tweaks I've tried.

Herbie's Audio Lab grungebuster materials
Machina Dynamica Clever Little Clock
Marigo Audio VTS dots and bands
Xtreme A/V QuickSilver contact paste

Realtraps Mondo Trap, Mini-traps, Mini Traps HF!
Measuring tape and painters tape for positioning speakers
2 8foot ground rods pounded into the ground

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..........

Try putting weights on top of your components and speakers. I have two five pound weights on my sony receiver and one five pound weight on my satellite receiver and three sand ceramic tiles on each speaker. You have to move the weights around in different spots to get the sound to your liking and this takes some time to get it right but when you do... your never go back!.................

I'll also recommend Herbies tweaks. Another tweak with dramatic results is Walker's SST silver electrical contact enhancer. A freebie is to freeze your cables over night - done three times - and there will be an audible improvement in clarity, imaging and soundstaging - it is not subtle and improves after about 10 hours of use. I know it sonds crazy. And, I don;t understand how it works, but it does. A simple experiment on your onw will demonstrate it to you first hand.