If your subwoofer is powered, then yes, connect directly to the preout. If it's passive, you will need an external amp to power your subwoofer. Connect an RCA cord to the amp form the subwoofer preout.
The extra posts are the "B" posts. Yamaha and most reciever companies have A and B channels for the fronts. The most common use it a zone 2 or outdoor speaker. NOTE: These posts have the same amplifier. DO NOT connect 2 separate sets of speakers and run them at the same time. It will be to high a load for the amplifier and if turned up enough, cause it to shut down and go into protection mode.
For more detailed answers about your receiver, consult your manual.
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