Yes, it sounds like the digital inputs are not assigned. If the digital audio from the dvd player is connected to digital input 1, make sure digital input 1 is assigned to the dvd input (or whatever input you plugged into); same for the cable box.
As far as digital sound from the digital cable box, NOT ALL CHANNELS ARE DIGITAL (I learned that the hard way a long time ago).

You should also connect the analog audio outs from the cable box to the receiver. Most receivers also allow you to set Auto (it determines the signal type and switches to the right input jacks) or Digital only or Analog only. In most cases, you want it on Auto. If the digital signal is present, it will use that; if not, it will automatically switch to the analog signal. If you happen to have it on Analog only, then you will hear nothing if the station is broadcasting digital only (rare, but might happen).