Are you primarily listening to the R5 while on the gym equipment? 3 feet sounds kind of high for a floor standing speaker, but I suppose that not only are you on a treadmill but also standing. 2 feet should get enough height without being a falling hazard and will likely look better than having them up higher. They're 42" tall after all, with the plinth. Keep the outriggers in mind when looking for a stand. That might make a stool too small and small table a better choice unless you remove the outriggers.