Your most indispensable "tweak"?

1) Great Cables
2) Stabilant 22A (From Concentrate Stabilant 22)  https://smile.amazon.com/Stabilant-5ml-Kit-Makes-30ml/dp/B001E50GQS/ref=sr_1_2?crid=2VZVB6OK4366C&dchild=1&keywords=stabilant+22&qid=1601662310&sprefix=Stabilant%2Caps%2C177&sr=8-2
Brand: D.W. Electrochemical
  Nothing better
3) Placement of Speakers, etc. 
4) Isolation

Definitely dedicated 20 amp circuit. I don’t think this is a tweak but adding a minidsp to eq my subs was also a game changer

Ear wax remover
Shunyata power cords
room treatments

Sorry for the plug... I have a PPT Mat for sale on Audiogon now.

ozzy

I don't know if everyone will consider this a tweek, although double shotgun speaker wires were mentioned, but for me the best tweek has been switching to the "Doug Schroeder Double IC Method".  Nothing has come close in SQ to doubling up my interconnects.