What is the best tweak?

I would rate power cords and isolation as the first areas to concentrate on. By searching for bargains on used stuff, you can economically address all these issues in increments, and realize the benefits for yourself.

After room acoustics, it's probably dedicated lines.

I gotst' all the equipment I need right here my friend. My favorite tweak is puttin' that equipment to some good use. Nothing like the nasty to put me in the mood for listening. Everything sounds better after dockin' your Johnson in the tunnel of love. I guess that falls under "other".

Other than that "other", the Room Acoustics/treatment is going to likely have the potential for a far greater effect than any other tweak you mention, unless you happen ot have really bad power in your area, in which case conditioning may have a significant effect as well. Not that the other things are not capable of making a difference. I just think that difference will be smaller and less significant. IMO of course, the room rules!

Marco

There is Not Any 1 BEST Tweak for ALL Systems - I feel!
Tweaking, as the word might describe, is Trying different things ( comparisons ) to see what Works/Sounds the best.
I have had Good Results with Some of Them and Not with All of them.
Its the 'SUM OF ALL THE PARTS' for a great sounding system!

Room acoustics is very important and can be very expensive (is that a tweak?). I've found that speaker cables are critical to the sound of a system so that would be #2 (could also be pretty expensive). For lower cost tweaks, isolation devices on cd players do make a significant difference.