FYI - you can use Basecamp or other open source tools to assemble all the .img files into a single one.
also, i haven't tried Orux with an actual purchased Garmin file, i read those didn't work still though that might be old info.
i have to give an opposite opinion from gahi, i still find the Orux ".img" rendering engine to be all but completely unusable. i think it's great that they are working on this feature, but my test of the main AZ Topo map from GPSFileDepot in Orux was a mess. you can barely distinguish a 4 lane road from a contour line, there are labels everywhere with no distinction between what should be a tiny elevation number and a major feature, and hardly anything is color coded or thick/thin based on importance. maybe it was just this map, but it does render fine in Basecamp and on Garmin devices. just my 2 cents.