Since you have HDMI ARC just connect the PC to an HDMI port and the HDMI ARC to the TV on a receiver that supports ARC, and you should be able to properly decode surround without any problem.
I am using an old i3 system with a gtx760 2gb on my 4k set, and unfortunately my trusty old Onkyo 5.1 does not have ARC so I am stuck in the stone age with an optical cable from my TV to the Onkyo. Decodes 5.1 well enough for my needs, maybe I will upgrade at some point.
Bottom line, you just need an ARC capable receiver and speakers to connect up your PC and TV. Or do it old-school like I am doing and connect optical out from your TV to a non-ARC receiver. Should not have to connect the PC directly to a sound source, it's a hassle since most TVs are "smart" and can do apps that render the PC / receiver connection useless.