I don't think it depends on CinGG. Even Steam has problems with 10-bit
(crashes!). Other programs (Firefox) show no difference between 8 and
10-bit, and others work fine at 10-bit (mpv). No differences both X11
and X11-OpenGL. I think the basis is always the lack of color
management of various programs.
Not exactly color management as ICC profile application but basic fact images use 10 bits where they used to have just 8 per channel!
To create a new X server: sorry; you ask too much of my rusty little
brain! Anyway it's a matter of renaming the 20-amd.conf file to
20-amd.conf.back and rebooting, it's not very long.
I think you can try and start second X like this:
X :1 --depth 30 &