Available is another great low cost tweak with truly impressive results:
About the AC Tuning Stick
"The Purpose of the 6" long AC Tuning Sticks are to stabilize EMI and lower the noise floor in your audio system. The AC tuning stick's contents (embedded crystals, magnets and carbon) are stabilized with black resin, a material which sufficiently suppresses microphony effects. Included also with the AC Tuning Stick is a metal foil sticker that is Quantum treated. This sticker works on the quantum level and is comparable to the WA Quantum products."
"Recommended usage for the AC stick is to plug it in close to your equipment. A vacant spot in a power distributor makes for a convenient landing place. It would appear that the tuning-stick concept uses access to signal and AC ground via a connector's ground pin to 'drain' or otherwise affect noise riding on a system's ground plane."
What you will hear:
"You will hear a more natural timbre, with a remarkably finer vocal display. The flow of the music is less electronic, and more organic. The ambient information contained in the music seems to be more evident at well, which again adds to the naturalness of the sound."