First, we don't allow discussion of Navi-X on xbmc.org
Second, no offense, but if you're going to buy hardware, especially hardware that is considered to still be in-development for XBMC, you should really research this stuff before buying something. I don't say this to be mean, I say this because there are a lot of people looking to make a quick buck from XBMC for Android, and some sell very poor quality boxes to people with very poor support. XBMC for Android itself isn't considered completely "done" yet, so there's also beta-like issues that might be present. YMMV.
You need to visit the G-box website and download their special build of XBMC. Currently, due to XBMC for Android still being in development, any box that advertises as being able to hardware video decode in XBMC will need to use a special build and not the "general use" one provided from XBMC.org. There might be other sites out there with experimental builds as well, but you're basically looking for one that supports "AMLplayer" or "AMLogic", as that is the type of chipset inside your device.
Also avoid using wifi, as the wifi chips in most Android set-top-boxes are not very fast or have very good range. Some are better than others, and some will even let you use an external USB wifi adapter that can be of higher quality.
Be sure to also check out the
Android FAQ (wiki).
Thank you and enjoy your flight.