The power that is required to run a subwoofer properly is (typically) much more than any A/V receiver will put out or designed for. So, you will want to get a decent amplifier designed for subwoofers. You will then use the LFE output on the Yamaha, run it into the outboard sub amp, then the amp will power the sub.
Since, you may find this to be a pain the rear to setup, you now know why so many subs come with built in amplifiers that are perfectly matched to their particular sub.