Tweaks and upgrades that aren't gimmicks

Room treatments and electrical upgrades. If you spin vinyl, a vacuum powered record cleaning system is a worthwhile addition.

hmmm, this could be quite a list:
1) room treatments
2) dedicated AC outlets
3) vibration control (esp beneath moving components (like CDPs or turntables, but highly effective under ANYTHING with a toroid tranny)
4) power conditioning...depending on the unit.

rc

My biggest sonic improvement came when I experimented with bi-amping.

Splitting the loads between amps on extremely difficult to drive speakers has just made everything move in the right direction. In short, everything is better,

I also bi-amp a very efficient speaker system, but the sonic benefits weren't nearly as great. To be sure there is some improvement, but you would never justify it on a cost benefit anaylsis.

Hope this helps ...

Jerry

Two relatively inexpensive tweaks that I really have found to work are the Blue Circle Noise Hound III and the Totem Beaks.
The BCNH I tried between source, pre, amp as well up-line. I found the effect the best right before the source, as well as up-line, several feet before the source. Quiter back ground, better resolution. (note, I can not try them down-line, as there are no more receptacles.)
The Totem Beaks, (one set of two, although Totem claims even better results with a set of four) when placed at the front outer corners of the speaker, about 1.5" in from front and side, provided a great improvement to my HT speakers (Athena.) The immediate improvement was focus, less smear, more depth to the sound stage as well as some width to the s. stage. You can actually feel them working, vibrating ever so finely when touched.
I can not comment how they work on my Gershmans, as there is no room to place them on top.

Instead of two stereo speakers in the front, try four identical stereo speakers (two left, and two right),(two in the center, and two outside). Play all four at the same volume so no separate attenuator will be needed. Angle the center speakers outward until the whole wall lights up as one picture of sound. At present your wall probably sounds like it has two "bright" spots with a hole in the center. If you think two speakers give you all of the detail, separation, and focus that you need, you are going to be in for quite a surprise when you try four. There are no gimmicks involved. It's only two channel sound, but it sounds better than SACD using digital decoders. That's my two cents worth.