(1) I’m not too sure about that simply because the audio and video are synchronized first on the capture card and then sent to the audio and video card; plugging it directly into the soundcard may result in the audio coming before the video (strange delay).
(2) I believe Realtec is an on-board soundcard, am I correct? On-board soundcards are often times problematic, especially when it comes to drivers. So it’s more then likely that a regular PCI sound card will have better performance.
(3) Since this is also in relation to your capture card, I’m not 100% sure. I have that same exact capture card, but I hardly use it, so maybe someone more knowledgeable about the combination of these two can help you. I just know that these drivers have fixed a few problems on my end.
If you do decide to get it anyways, here are the drivers (scroll down to “download link”):
kx audio drivers v3538
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