If your grid is going to scroll then the 2D API would be your best bet. If not then imagecanvas will do. You can also wait if you can, for Scene Graph to be released. The built in grids are not designed with that kind of flexibility. If you want to see what the 2d can do you can check out my demo channel in my signature below
As a matter of fact the Joel Channel (not yet published) that I was recently working on is exactly the design that you want with a selectable Hero and one row grid on the bottom
My Channels: 2D API Framework Presentation: https://owner.roku.com/add/2M9LCVC
Updated: 11-11-2015 - Completed Keyboard interface
The Joel Channel ( Final Beta )