You can mark a thread 'solved' by going to the 1st post, click 'thread tools' (above the post to the right). Then select 'Mark this thread as solved'.
*edit- 'thread tools' will be above the 1st post on every page, you dont have to go to page #1.
For HDMI with audio the sound is routed through the sound card.
So the video card/GPU has a mixer.