Your most indispensable "tweak"?

Power cables, interconnects and speaker cables.  Without them, I can’t get my system to work.

What did it for me more than anything else was a proper equipment stand (Sound Anchors) custom built to accommodate my anti-vibration platforms with my preamp on top of one, and the turntable on top of the other. The stand is in turn seated on a set of Aurios Pro bearings (unfortunately nla).

This combination allows the system to play at any volume and remain relaxed- even at 110dB (according to my Radio Shack sound pressure level meter).

High Fidelity Cable- any of their wave guides plug ins

@68pete what did these do for your system?

@needfreestuff I finally dialed in my sub to a crossover and gain level that opened things up so much. Not an easy task. 

redwoodaudio
There is a big thread on them here in the forum. They simple made the sound so much cleaner sounding across the board. Back around vocals where much stronger, able to see deep into the sound stage. More black space around the sound.