Nice setup
It sounds like you have put together a great system.
Not sure the model on the Rotel amp, but it should have plenty or power and more than the Yamaha for powering both the highs and lows of your speakers. Unless the amp has a volume control, you can't bi-amp using the receiver and external amp because you cannot match the SPL level of the highs and lows. Also, different performance characteristics of different amplifiers make this undesirable. Connect the receivers preouts to the rotel, run the auto or manual setup, and enjoy.
Feel free to read a few AH articles on the subject, but there is no performance benefit to biwiring. It effectively increases the gauge of the speaker wire. I would recommend Belden 5000UP speaker wire from westlake electronic. Buy some banannas and techflex to dress it up. Buy the 4 conductor version to biwire or biamp. It is also suitable for in-wall wiring.