I'm confused with 2 ohm and 4ohm subwoofer. I want a single 10in subwoofer. I have a Alpine Mrv-M500 amp. 500watts @ 2 ohms and 300watts @ 4 ohm. I've been told I want a 2 ohm sub to get the max wattage of my amp. Car Toys and several other car audio places tell me I need to get a 2 ohm...