Greg, the amp will be fine if it drives 8 ohm speakers.... 10 ohm/8ohm is a theoretical value, the impedance will vary depending on the load put on the speaker. The only thing is: the orginal subwoofers have a pretty good efficiency (don't know the number) and if you are to replace them with lower efficiency units, it might effect overall SPL (though you will have somewhat more power available due to the 2 ohm difference).
Good luck mate... has been a while!