Sorry for the delay in the response.
When you set the amps 'channel' to the HDMI input that's coming from the PC, and then the input on the TV that's connected to the amp, the amps basically acting as a video source pass-through**.
Essentially, it's the amp that "sees" the PC, since it's receiving both the video/audio signal.
Hopefully this breakdown makes the whole process a little easier to understand (I'm even starting to lose myself

):
- Onboard audio is 'passed through' the GPU via the 2pin cable that connects the motherboard to GPU
- GPU with the DVI>HDMI adapter +HDMI cable transfer both the Video and Audio signals to the amp.
- The amps 'channel' input that is selected ie HDMI 2 , processes the video and sound. Resulting in the sound playing through your Home Theatre System
- Then that same 'channel' on the amp will then output the video signal to the TV via whatever 'video out' output you use, resulting in the Video being 'passed-through' the amp to display the signal on the TV.
Basically the biggest difference between HDMI and DVI is that HDMI is designed to carry both digital audio and video signals on the same cable. DVI cables are only designed to carry video signals. Since your GPU only has DVI-D outputs and no native HDMI outputs, the right adapter is needed.
This is why a DVI Dual Link adapter is important because there are plenty of DVI>HDMI adapters (not dual link) that will only carry the video signal and not the audio as well. By using a Dual Link adapter, this allows the 'extra' signal, in this case audio; to be transferred alongside the video signal via a HDMI cable.
**"Pass-Through" is a term used when a device allows a signal to travel through it without doing any processing. A middle man/conduit if you will.
With your setup, the sound is being 'processed' by the onboard audio - "Passed-through" the GPU and then delivered to the amp. The video is 'processed' by the GPU, "passed-through" the amp and the signal delivered to the TV.