In line with LinuxCanuck's advice, I went ahead and scrapped Ubuntu
Studio entirely, and installed Mythbuntu. The installation process
for the Myth TV modules was FAR easier, just as he had said! I also
discovered that the primary reason that "mythfilldatabase" wouldn't
run was that I had not yet set up my account with SchedulesDirect, a
deficiency I have now corrected!

The major problem I am now encountering is that Myth TV cannot find
the card in the system. This is probably because my Air2PC card is a
first generation model. The Ubuntu online documentation I have
perused indicates that, while this particular card IS supported,
firmware has to be downloaded and installed, apparently via the system
terminal. Has anyone had any experience along these lines? I'll do
this alone, so to speak, but I would appreciate some guidance.