Yay! It would seem that with the latest updates to the xc3028 tuner driver, my DViCO Fusion Dual Digital 4 (USB id 0fe9:db78) can use the newest drivers again.
Up to my last attempt at tracking the newest drivers, loading them would cause a system hardlock, which isn't particularly helpful on a PVR. Well, whilst the olympics were on I don't suppose it mattered that much. Komkommertijd, as we say in Holland.