Reverting back to the pre-rooted stock 4.1.2 firmware from this forum, in the hope that Titanium would happily restore everything without needing the "migrate system data" option didn't work, sadly. The phone got stuck in a boot loop, and reflashing the PARAM file didn't fix it. So, it looks like I'm stuck with CM11. Serves me right for jumping straight in with both feet; no-one else to blame but myself.
However, it looks like the Titanium backup is in SQLite format, so all is not lost. I've managed to dump the data table successfully, so all I need to do now is parse it for importing. But that can wait for another day, as the rest of the house has finally woken up and it's time for breakfast and presents.
Merry Christmas, everyone.