Hi Frans and welcome to the Forum 
Whilst this forum is principally geared towards UK equipment I will attempt to address your problem. Perhaps if anyone else from your country reads this they may be able to help more.
I assume that you mean Scart cable, in which case you will only be able to view the digital Cable channel on the DVD that the Humax is tuned to (or playing back), unless your DVD also has a digital cable tuner. Set the DVD recorder to the Line input that corresponds to the scart socket the lead is plugged into to view or record to DVD.
Note that you may not be able to record HD broadcasts to the Sony recorder.