interfacing

I've seen some ads regarding DVB-T tuners för Comand and on Ebay. They seem to cost around 300-400 euros. What kind of interface do they use to speak with Comand (assuming that you can change channels etc. using the Comand keys)? If it's all analogue output then wouldn't it be possible to use...

I've been looking around at the interfaces which allow you to pipe video into a (D2B) COMAND - i.e. they act as a fake TV tuner. The ones I've seen so far seem to plug in via the C1 and C2 connectors (with just a few wires connected), but there is no piggy-back/daisy-chain - so does this mean...