Any amplifier on the market can drive an 8 ohm load. Amplfiers only run into trouble driving low resistance loads. At 8 ohms, you'll only have about half the power of the amps 4 ohm rating, but your amp will thank you. It will run nice and cool.
cool, but not at peak efficiency. most car amps that are class AB are designed to be at peak efficiency at 4 ohm loads. Some amps are only rated stable from 1.5 to 4 ohms in fact, so look at the particular amp to see it's spec'ed range of operation.