Forgive me for the newbie question but: What are the differences between receivers? I see there's a Hr24,Hr20 a 500 a 700, etc... Currently I'm with Dish and thinking about going with Direct (NBA package), but don't know one receiver from another. I have a 722 now, so would love the bigger hard drive, so would that be the 700? And DTV doesn't allow external HD's - right? Any advantages (besides HD size) between all the receivers out there? Gonna go with the multi room view and HDDVR (if I switch). Thanks very much.