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.