I have a spa 4 body sprays, handheld, rainhead shower and installed a Kohler K-2971 Pressure Balancing valve with a K-728 transfer valve. The tempeture fluctuates a lot. I also have a tankless water heater. I read that pressure balancing don't get along well with tankless heater. This happens even when using one showerhead. So I think I need a thermostatic valve. But before I invest another $500+ I was want to get some opinions.