Sorry, I don't own a HUB, but I do know a little bit about the HUB and themes...So I will share what I know.
Many theme developers are not working with the current HUB FW as it is not compatible with .PNG file type or the .JPG trick. So you may want to do a FW rollback to 2.07 FW I believe. Just google "Firmware rollback for Western Digital HUB" and that should bring up some info on the process. There is info available on loading themes to the HUB but I cannot give you precise info on that as I do not own a HUB. I know how to do it on the SMP.
When selecting a theme - decide if you want to generate sheets via Thumbgen or not. It's a very easy piece of software to use. That way you can tweak what cover art you use, movie info and what templates you'd like to work with etc.
Tinwarble has an excellent Thumbgen guide for the Mojo available. (A text document and video on YouTube detailing the steps.) There is also documentation on the Thumbgen site. Just google "Thumbgen" it will be the first link. Sorry I couldn't be of more help, but I'm writing this on my phone so not easy for me to dig up links.
These steps will be a good place to start/research.