Great news, earlier this week Yamaha Japan released a firmware update for the RX-A4A, RX-A6A and RX-A8A AV receivers. Once you apply the update you'll be able to pass a 4K/120 (up to 24Gbps) or a 8K/60 signal (up to 40Gbps) through the top 3 Yamaha Aventage AVR's!
On top of this, there is now support for HDR10+ and more which is coming soon!
If you are using a 4K/120 or 8K/60 capable device with correctly spec'd HDMI cabling and a display that supports the 4K/120+8K/60 formats, you will need to make a change in the AVR settings in order to pass the signal through.
To enable the new formats:
Simply navigate through the AVR menu and select 'Video/HDMI'.
Choose 'HDMI Video Format'.
For the HDMI port(s) that the applicable sources are connected to, ensure the video format is changed to '8K Mode'.