Your most indispensable "tweak"?

On a related topic, when I see
"WAF" (wife acceptance factor)
in a post, I get a warm happy feeling.
And I thank my lucky stars, knowing this
will never ever be a consideration for me.

In sales, the best way to handle an objection 
is to eliminate it, up front.

Lots of money

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