A big problem you have is that Bose does not publish any meaningful specifications. Might not be a big deal if you’re “keeping it all in the family” with Bose gear from top to bottom, but when you start “mixing and matching” you run into issues. For instance, with your 791s, we don’t know if they’re 8-ohm or 4-ohm. It’s really hard to pick an amplifier without knowing that information, especially for running multiple sets like you are.
Regards,
Wayne A. Pflughaupt