I would also vote for option #1 running your 2-channel setup in bypass mode. While watching films and TV, you'll be less sensitive to differences in the sound between your mains and other speakers anyway, and this won't compromise your 2-channel playback.
Ignoring the sound character for a second, you should pick an amplifier's power output for the other three channels based on how hard the speakers are to drive and what volume you want to achieve. I'm using a Bryston 21B3 as a 3-channel amplifier, as it is one of the few 3-channel units that is capable of high power output and drive.
Ignoring the sound character for a second, you should pick an amplifier's power output for the other three channels based on how hard the speakers are to drive and what volume you want to achieve. I'm using a Bryston 21B3 as a 3-channel amplifier, as it is one of the few 3-channel units that is capable of high power output and drive.