I tried searching, but didn't see exactly the answer I was seeking. I got a HR20-100S, but wondering what are all the possible sub-models for the HR 20? I have seen mentioend HR20-700, 600, etc, etc. Briefly can someone summarize the different HR 20 submoldels, what they stand for and what are the differences? Is the sub model desingation a factor of the date it was made, where made, original manufacturer, software updates or what? Which is the best? Thanks for the info. I was lucky enough to get the HR 20 that I requested on install because of the OTA, so trying to use the forums to bone up on it.