Hi Krize , I'm on the same boat as you (using VGA666 adapter on a CRT TV). Did you find a proper solution to this?
My current workaround is using Batocera as it supports VGA666 out of the box, and then run Kodi in there (comes pre-installed).
HI, Honestly, I really don't understand why you want to use that CRT display. It's so outdated. Power hungry and the picture quality is worst than any cheap flat display... So, you should really think to forget that CRT with "signal adaptation chain" (+ picture problems) and switch to a flat display with a simle HDMI cable.
CRTs have better motion clarity than any "flat display" because of the way it refreshes the image (electron beam). Certain things just look objectively better on a CRT (mostly retro games but also some TV shows if they were released with an interlaced format).
Telling a CRT user to switch to a current HD display is like telling someone who plays Doom to upgrade from Win95 to Win11 because Win95 is "outdated" when Windows 11 doesn't even have a DOS mode anymore. Certain things were meant to be used in a certain way.