Can’t get Apple TV into 4K HDR

Just bought Apple TV 4K. I’m running through Yamaha RX-A860 receiver into Samsung 4K tv (KS8000). I updated firmware on both devices and changed TV settings to accommodate 4K HDR, yet every time I try to switch to 4K HDR, atv kicks it back to SDR. I haven’t tried running straight into TV because it would be a pain, but I’ve read elsewhere of issues running through receiver to TV. Anyone else having this issue and does anyone know a fix?