Your most indispensable "tweak"?

+1 SR fuse

Well, after 30+ years in construction, and the hearing loss that results from that, I'm going to say "cupping my hands behind my ears". Not kidding, try it. Sound-stage instantly becomes all-encompassing, details are greatly expanded. First time I tried it, I was both amazed and a bit bummed. Take care of your hearing, should go without saying.

Dedicated Apollo turntable shelf, mass loaded Atacama speaker stands, QED biwire speaker cables, Audioquest NRG power outlet, Niagara conditioner, 20 amp dedicated circuit, AQ thunder power cable. Recently, Origin Live Gravity One record weight, yet to try, but looks interesting.

I run shotgun bi-wire cables with spades to my speakers, but adding jumpers in the banana connections as well significantly improved imaging and tightened bass to the point that I won’t listen without them. 

Upgrading my Power Conditioner from the Niagara 1200 was a huge leap for me.