Assuming the ceiling is 8 to 9 ft and you sit 10 to12 ft from the speakers you will be fine with the 510 or 710. I know the SR7009 has no trouble driving the Silver 8s and it is only slightly more powerful than the 710.
If the speakers begin to sound less than good, turn the volume down a little and nothing will get damaged. 4 ohms is only a problem if you over drive the receiver, but you have control of the volume button/kno, right?
If you still worry, there are avrs that are more powerful, or you can add a low cost 2 channel power amp to drive the front L/R.