What i did is i put the normal shader-slangs (how was it called? I don't have my pc on right now so I can't check, but it's the shader folder you can get from the official retroarch resources) in my sd card root, then put the compiled wii u shaders in the same folder. Then I opened RA on wii u and manually set the folder as the default shader directory in the settings, then i was able to use them. Regarding that bandlimit shader i'm not familiar with shaders in general, so i haven't tested that one
You wouldn't happen to know of any resources that would help me out with this do you? I hate to ask such basic questions, but I can't for the life of me find the info I need, nor would I know where to start. I just want crt shaders on my WiiU Retroarch :/