I don't think those would fit the "mission" of this, but they can be solved with a Fusion Brain. This does just volume control and in a way that you can still use the software buttons or this at the same time, without them getting out of sync. Like with your potentiometer, you can control the volume up and down on the PC, but it is always limited by the pot. Or you can control the volume by the pot, but you are limited by the PC. This gets around that.
As to having it mute when no ACC present, hook up a Fusion Brain with a resisitive divider input into one of the analogues. Then in software it is as simple as keep it in mute when the input is low, or so many seconds after low, or whatever you want really. It solves that problem separately but better.