Yeah, the more equipment it has to go through, the more the distortion that could be created.
You can go through the HU, but if you do, don't got beyond 75% volume on the computer and HU. (and you may need a line driver between the HU and the computer, depends on the voltage the audio outputs)
As for touchscreens, IDK. I'll do some research, but I've honestly never seen a 10" touchscreen. I've seen 7" and 15", but that's the closest I've seen.