Currently, I am not reading in a pix_texture or the active GEM texture to publish, I am simply reading the screen, but its a useful feature to capture the entire scene as rendered so far (you can control what it captures by adjusting the gemhead layer ordering).  Nor have I made a 'client' version that outputs a received texture from another app, but now that Hans Christoph helped me sort my XCode issues, I suspect with some help we can have a fully working Syphon implementation for GEM quickly enough.