Sorry for necroing this up, but I've been sniffing around in the code since I was fussing with this plugin today (I'm interested in the gameboy color mode algorithm maybe being tidier in the Max version, closer to the isolated gameboy color output plugin). My code literacy is very minimal, but as far as I can tell the shader parameters are in line 15, but Plus doesn't call for that variable anywhere so it's not just a matter of copying that line. My next idea was to copy most of the body over, but like you I don't see anything happening when Max is on (even with no other plugins), so like I'm not sure what to translate over to make parts of Max work without making Plus not work.
Not to ramble on, I guess most of that is unimportant. Did you ever get further direction on how to get Max to function by copying segments to Plus?