HDMI 5.1 Surround Sound?

[HelicopterHands]

I'm trying to get my 5.1 surround sound system to work with my PC. I have both an HDMI cable, and an optical cable. How would I go about getting full 5.1 sound (including back speakers) with a few HDMIs? When I try connecting an HDMI from the PC to the receiver, and the receiver to the TV, the resolution scales weird. Also, "NVIDIA HDMI OUTPUT" is "not plugged in."

Any help?

Running:
-Windows 8.1
-GTX 970

 

[getochkn]

What receiver

 

[getochkn]

What receiver