This tweek is not cheap, but it won't cost you anything either, provided you qualify by owning an unused pair of loudspeakers. It comes from some audio manufacturer, I forget who he is, and was published in Stereophile.
The tip is to placed an unused pair of loudspeakers in the corner of your listening room, behind the loudspeakers. I tried this with a pair of Linn Kan II mini monitors placed directly on the carpeting. It seemed to make a small improvement, though nothing major. After listening this way for a few months we had a minor plumbing related flood and I had to move my LP's to where I had my Linn speaker stands stored. In the process I moved the speakers stands into the rear of my listening room where the Linn's were located and place the Linn's on top of the stands.
This produced a nice improvement to image placement in the soundstage and also added weight to the presentation. Really very nice. If anyone is interested I could look up the article and elaborate on why this works. Let me know.