Connecting mac osx laptop to denon avr3300W..no audio

Open the System Preferences item under the Apple icon at the left end of the top menu bar. In the window that opens click on the "Sound" icon near the right end of second row. It will show you the available outputs for system sound. If there aren't any available other than the internal speakers It's a problem with the connection of your device to the laptop.

All I see is "internal speakers" and "LG".  I selected "LG" and still no sound.  

My brief research on your AVR shows that due to its age it doesn’t have Bluetooth or Apple Airplay capability. This would be required for wireless streaming. Also my older Mac had video out of the HDMI but only more recent ones output both video and audio through HDMI. Another option is to buy a Bluetooth receiver that you can stream the audio from your Mac and then digital out from BT receiver to the AVR. These are available in many places such as Monoprice. I use this in an extra system and stream from iPhone iPad or MacMini. Good luck.