The RTS couplers now being sold by Audio Horizons. They made a nice improvement in making the bars solid over hollow like they once were. They are definitely additive--the more components that you couple to the shelf, the bigger the difference in sound. The drawback of these couplers is it takes about 7-14 days until you hear the dramatic improvement and they continue to improve for awhile. Initially there was no difference other than each component is now securely clamped to its shelf. I have Sistrum racks and platforms which already made a big difference in the sound. The RTS couplers made an even bigger change. I use them on each component except the turntable. If you are skeptical, I understand. If you don't try them, it truly is YOUR LOSS. No other thing I have ever done to my system has ever been as big of change for the good--no drawbacks in sound.
Your Best Tweak Lately
My latest, and perhaps best tweak, is a continuation of fuse upgrades, first using HiFi Tuning, two types, then Furutech, and finally, Synergistic Research Reds. Now, you may not believe in fuses, and that's ok---not here to convert anyone, just to report that these SR Reds are so far ahead of the others listed--to my ears, at least. If you have Maggies that you want to easily improve, put these in. I also have them as the mains fuses in ARC 210s and 861GNSC. If you have confidence in your power supply as stable and plentiful--another tweak in itself--no worries about the safety of these fuses--I even push the ratings a bit to match my big-gauge power cord capabilities. In the Maggies, I push them to 8A and 16A (stock is 2.5A and 5A) for a more "straight wire" effect by way of the bigger elements--incredible upgrade without molesting the speakers. With potentials in power supply, cords, cables, isolation schemes, room tricks, etc, this is a tweaker's paradise--I'm stealing the term back--just for audio.