Can’t Enable Dolby Vision On New Apple TV 4K

Hello,

I just received an Apple TV 4K for Christmas and I can’t it to enable DV. It asks me to test my system, and it just hangs on a black screen with the message:

AV Receiver is conncerted to HDMI 1

AV Receiver has no video signal

I have an Onkyo TX-RZ920 & a Vizio M75 E1, both with completely updated software, and high speed HDMI cables from Monoprice.

Any help would be appreciated!