How many DVR's do you want? You can do 1 HD and the SD from a 722 DVR and get unlimited storage with an external HD at no additional charge. You can do the other 2 HD's with a 211 series in each room. the plain 211 has a built in OTA tuner the "k" requires an OTA tuner module. Same goes with the 722 "k" but that gives you 2 OTA tuners. The 211 can be turned into a simple DVR by adding an external HD for a 1 time fee of $40 eliminating the monthly DVR charge. It also gives you the ability to pause/rewind what you are watching.
The 211K does not have the requirement of an OTA tuner module. It has a single OTA tuner built in.... The 722K does, indeed, require the module to receive OTA channels.