I can't speak to this particular issue at the moment, but I can tell you that I ran X1 on a machine using the on-board graphics processor, and had no graphics-related issues.
I don't know anything about R-Mix to guide you one way or the other. If there are indeed any graphics issues, I have used and others as well, cards as cheap as around $50 with good results.
My current computer is a behemoth with really high-end cards - but that was just a bwa ha ha I'm taking over the world moment of purchasing on my part, and not at all needed.
You should have PLENTY of power to run things.
Please elaborate on the problems you are having.
Hope this helps,
Bob Bone