Hey Eddy, did you ever get this to work? Sounds like you are trying to do the same thing we're trying to do.
We've got everything working, including hosting content on AWS/Cloudfront, but can't find ANY documentation that actually says how to call the Grid Screen and get it to show instead of the poster screen.
I'm sure it's just because I'm not much of a programmer, but it can't be so difficult that even Roku's own SDK guide doesn't even mention the Grid Screen existing (in the design section). Anyway, if you figured it out we'd really appreciate any tips, it's the only thing stopping us from launching.
Thanks!