This is sometimes even more pronounced on a typical HT system with a Cable or Sat box if you compare the volumes of the analog (lower) channels to the digital (generally, upper range) offerings. FWIW, anything coming from my Motorola Comcast DVR box in DD5.1 would have to be really cranked on my Onkyo receiver to be able to hear it properly.
There's really not much you can do in this case, just get a sense of which channels require the volume boost, esp. for visitors using your system ;).