Short answer: You're not going to be able to able to meet your requirements without a mixer. You need a mixer to combine the singing and music before it gets routed to the Yamaha. It could be something as simple as this

https://smile.amazon.com/gp/product/B01N6448Q4

or this

https://www.amazon.com/Soundboard-Interface4-channel-Bluetooth-Streaming/dp/B0B884KR1B?th=1

Longer answer: Your AV receiver and speakers were never designed to sing though. You could damaged them. I recommend a separate powered PA speaker, which are designed for singing. Although it is possible to connect a mic to the laptop using the mic input port I don't recommend it.