In addition to needing two five channel amps, in order to get "equal" sound, all five channels have to have the same power output. For example, some cheap HT receivers don't have as much power for the rear surrounds.
If this is just a convenience thing to get sound to all the rooms for mostly background listening, a switching box is probably a lot more economical.
If this is just a convenience thing to get sound to all the rooms for mostly background listening, a switching box is probably a lot more economical.