For the absolute best cable/floor isolation, take fishing line and suspend them from the ceiling. Space the lines a couple of feet apart and keep the cable a few inches above the floor. You might start with a good clear monofilament or fluorocarbon line at 10lb test.
Then try different line strengths and colors, and heights off the floor to get the best sound. Clear tends to sound the most transparent, and saturated colors sound darker. The stronger the line, the more damped the cable will become, and that may sound heavy. Of course your results will depend on the cable, the floor surface and the type of music you like.
When dialed in, this approach is guaranteed to have the best performance for almost no cost, and provides much experimenting fun between listening sessions. For others who may have tried this already, please give the Capt some helpful advice.
PS, Be very careful, as these lines can be hard to see, and someone might get tangled and cause injury to themselves or damage to your equipment.
PSS, I am not associated with any manufacturer of fishing products.
