[bookman156]

You can't reference a font folder outside of an epub can you? Never tried.

Have you tried simply removing the Asian fonts from the epub and just specifying either serif or sans-serif as font family? The epub should pick up the Chinese or whatever font from the system. If you only have, say Noto Sans CJK TC, and that has the characters you need, then that should be what you see without need of specifying a path. There is no need to embed an Asian font, and if you want a particular one just make sure that's the only one you have on your PC (or see whether you like the one that is automatically selected).

You could also try specifying font-names in the font-family list that you have in your local fonts folder in Windows and see whether they get picked up, but if you're satisfied with the Asian fonts on webpages then that should be what you see in an epub simply by removing the embedded fonts and without specifying anything save perhaps serif or sans-serif.