From a quick look: The different receivers vary in that one can be used to feed two TVs with different programs, another feeds two TVs and can record video for later playback. One is a single TV with video recorder and the fourth is just a receiver that feeds one TV.
So you have to decide if you want to feed one or two TVs and if you want a video recorder capability and then select that model of receiver.
So, if I have 3 tv's I will need 2 receivers. I guess that would leave me room for a 4th if desired.