Hi, John. Cable boxes come in all shapes and sizes, so there's no one-size-fits-all answer. Extra-Thick grungebuster Dots would surely be beneficial with most cable boxes. If the box is very light, Herbie's Audio Lab Big Baby Booties might be a better option; if full-component size and weight, TenderSoft Tenderfoot isolation feet would be ideal.
Steve
Herbie's Audio Lab