Onkyo HTRC460 PC Connection Limited to 1080?

Hello,

I borrowed an Onkyo HTRC460 AVR and I just hooked everything up today. I also have a 4K Samsung TV. The problem I am having is not fully understanding what 4k upscaling means, because I assumed that when I plugged my PC into the AV that it would retain my 4k settings within my graphics card; however, I am dropping down to 1080. When connected directly to the TV, Nvidia settings are at 4K; however, when I go through the AVR, I no longer have the 4k option, and I am limited to 1080 and lower. In the Nvidia settings my monitor is no longer listed as the 4k Samsung, but rather the Onkyo receiver, so I loose the higher resolution settings. Yet, the receiver has both 4k pass-through and upscaling, so why am l loosing the options for 4k resolution in my Nvidia settings?

I don't want to use the AVR for video now but if I disconnect the HDMI and use optical cables for sound only, I also loose better audio functionality that comes with the HDMI like DTS. Is this AVR just not 4k ready and the pass-through/upscaling doesn't actually affect resolution options in the graphics card settings?

Thanks