Hi Klk,
Please be aware that pointed cones are rigid devices and will not isolate your amp from floor-borne vibrations generated by the speakers. In addition, using only three pointed cones will leave two of the corners of the amp unsupported thereby allowing them to be more easily excited by air-borne vibration.
Rolling ball type of devices are also rigid in the vertical plane and will allow floor-borne vibration to be a factor.
Both pointed cones and rolling balls do not address air-borne or internally generated vibration so at best, they can only be partially effective.
Best Regards,
Barry Kohan
Disclaimer: I am a manufacturer of vibration control products.