What commerical audio system tweaks provide sound quality improvement??

They all change the sound.....its up to the listener to determine if it's better or worse.

hifiJones......Very true....and for many aging enthusiasts on these pages, it would be hearing aids.

Any, and all of the Audio Magic products. It began for me with the fuses. I now use AM’s Pulse Gen ZX’s, Blue Dot Disruptor, ac Power Outlet, Mini-Ref power conditioner, and Speaker Clarifiers. Every time I added one of the Audio Magic products my system improved. I highly recommend the AM PEA devices! I’m using three now, which have literally exploded my system’s soundstage, recreation of air, and greatly improved the natural tonality of all instruments, vocals included. Everything just sounds more real. You can’t go wrong.

A shout out for PWB Electronics, you know, all those things that go bump in the night and give audiophiles the heebie jeebies. The unspeakables. Peter Belt RIP.

speaker placement and system match is the best tweak to my system, then after market power cords like Shunyata brass spikes under subs and speaker stands, my speakers already came with stillpoints for the path stands, other than that i think the rest is snake oil.