Marantz AVR7005 vs Marantz AVR 606

Planning on using one of these receivers as a pre pro with an NAD T955. Looking at the processing ratings I can't tell much of a difference in the audio or video processing capabilities ... of course that is why I am a newbie to this game!! I do see about a $500 difference between the two. Can anyone help me with the specs and the differences?
Thanks!