Whatever "didgi box" output connection is made to an input connection on the Panasonic, that input has to be selected as the viewing/recording source.
If the input connection is composite yellow video, white/red audio, usually line inputs L1 or L2, that is the viewing/recording source.
If the input connection is RF then a "channel scan" should "find" that source, as long as the device providing the signal is "active," and that should be the viewing/recording source.
If the input connection is SCART then that connection should be selected as the viewing/recording source. That signal may need to be "active--I don't know. (I'm in the US so I'm unfamiliar with SCART connections and functionality.)
The DMR-EH50 Operating Instructions will illustrate and describe the connectivity variations as well as functional and operational procedures.
I don't own a hard drive equipped Panasonic recorder. (I own basic US model Panasonic DVD recorders.) I understand that the hard drive equipped models have unique operational characteristics with which I'm unfamiliar.