Your most indispensable "tweak"?

@patd33 - essential! 

@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. 

@hilde45 Too expensive!    

Yeah, there's been some good humor vibes in this thread. 

So many interesting suggestions!  Thanks all.  And feel free to keep them coming...

@highend666 - thanks for the link, although completely impossible in my listening space

@stringreen - details of your carbon fiber outlet please?

@sjsfiveo - yes, couldn't agree more about NOS tubes

@soix - not sure what these jumpers look like in action -- can you describe more?

@barbapapa - not familiar with PPT -- what does that stand for?

@chrismini - super interesting suggestion

So many isolation/shelving ideas too -- will look into those.  Thanks!

Interesting... nobody has mentioned anything from Stein Music...

So I picked up a novum pmr premium resonator on the basis of a recommendation in this thread (and other reviews) and the effect it has in my room is beautiful. Hard to describe, but improves tonality, image density, without any negatives. It's also quite beautiful to look at sculptural. I've since found a second one used and am waiting to receive it. Definitely got me more open minded about "tweaks". Love all the ideas here.