I am putting in a whole house audio system with multiple zones. There will be areceiver per zone. Some zones have more speakers than I believe the receiver can adequately drive. How do I figure out what kind of power I will be needed? For example, if I have 1 zone with a 100 Watt Receiver and need to drive 6 speakers (rated to 50 watts each), what size amp do I need? I know I could probably get by driving 6 speakers on a decent receiver, but I want good sound quality and good volume.