How can I connect my PC to a 7.1 channel a/v receiver when my motherboard doesn't have required connections?

[TechnologyHatesMeButILoveIt]

I know this sounds (no pun intended) like a easy question. But the traditional ways do not work for me.
I tried a optical cable, and the connection on the motherboard is bad. The sounds goes out and there is static. I know its on the motherboard's end because the a/v receiver works fine when connected with something else.
I tried a coaxial cable, but my motherboard doesn't have that connection.
I don't have any way to have sound now because I got rid of my second monitor, and it was the only monitor that would have sound. I cannot find a way to make my Samsung (UE590 Series 28" LED 4K UHD) have sound. It shows up as a sound option, but there is never any sound.
I can't even use headphones because the computer doesn't register it.
My receiver is a Yamaha RX-V581BL
My motherboard is a gigabyte GA-Z170X-UD3 Ultra
For months now I was just using my second monitor for sound. It sucked, but I didn't have time to deal with it. Now I can't stand it anymore.
I can connect my phone and my Samsung laptop wireless to my receiver, but I can't figure out how to with my pc.
My wireless card is a TP-Link Wireless Dual Band PCI Express Adapter TL-WDN4800
I have looked at sound cards, I even have one, but they all have the same connections as my motherboard but without a optical connection. Any other cards are $200+ .

Is there a easy, single cable solution? Or a wireless solution?

I built this computer (built two before it) about a year ago... Since thing I have replaced everything in it at least once, and sometimes three times, and have had four motherboards (First three were bad from the start) Nothing seems to last or is broken in the beginning. My $1500 computer has turned into a $4000 computer, yet its not worth that in any way.

 

[Kasper Jorgensen]

You can only do it wireless if both your receiver and computer have bluetooth.

Your options..

1. Your motherboard should have outputs for 7.1, you just need the analogue cables with mini jack in one end to fit your computer and rca in the other end to fit your receiver.

2. If your receiver is new enough it should have hdmi input, in which case you can transfer sound from your GPU.

3. Buy a new soundcard either as PCIe or external and use digital output from that.

 

[TechnologyHatesMeButILoveIt]

Using HDMI doesn't work for me. It just turns my TV into a second monitor. I would love to use the HDMI. But I don't know how to stop it turning my TV into a monitor without going through the trouble of pulling out the receiver, which ends up pulling out wires, to unplug the TV from the output. Doing this every few hours is too much.

 

[Kasper Jorgensen]

Guessing you don't fancy using analogue cables, your best option is to get a new soundcard.

 

[BFG-9000]

I tried a coaxial cable, but my motherboard doesn't have that connection.

That board has two pins labelled SPDIF_O. That's where you would attach an adapter for RCA coax,or SPDIF to optical.

The only difference between the two digital formats is one has an LED in it, so as in the above, you can get both from the same 2 pins.