yes the m500 is a one channel, mono amp. you take the wire running from the amp and connect the positive and negative ends to the corresponding ends on the first subwoofer. then, you take an extra piece of wire and connect the positive and negative ends of the first subwoofer to the corresponding ends of the second subwoofer.
no, i am not underpowering my subs SiLvAaCCoRdv6. im running the amp at a 2-ohm load so it produces 900 watts at peak. i never use all of it though. i keep my sub control to about 1/2 or 3/4 and it makes my whole car rattle. i only turn it all the way over when im leaving parking lots or whatever and it's extremely loud. my oem spoiler on my trunk and license plate both sound like it's going to fly off. also, my rear deck rattles so much that it sounds as if my rear window is gonna break (which i hope won't happen).