If your AVR has seven channels and your main room is only 5.1, then the two spare channels can run the rest of the house.
However, the second amp idea is preferable, since you are doing 7 speaker pairs. Let the outboard amp share some of the work or make sure that AVR has something to keep it cool.
There is no truth anymore. Only assertions. The internet world has no interest in truth, only vindication for preconceived assumptions.
