If the PC is deinterlacing and upscaling with a resolution set to 1920x1080 60Hz, then the receiver won't because it is receiving a progressive 1080p resolution and it would just pass it through. Now, you may have some unknown features turned on in your video card's drivers that can ruin the picture, such as edge enhancment, dynamic contrast, denoise or a form of color correction. Your receiver may also have a feature like this that needs to be turned off, as it would still process.
I do not believe there is any way to tell a PC to only output the native video it is receiving. You'd have to manually set the resolution each time before playing that video. People don't tend to mess with this because video cards these days are really good at deinterlacing and upscaling. Usually it is a driver/option set issue if it is looking bad.