I have an Outlaw 770 MC amp driving 5 ea. speakers.I have driven 6 before.
The amp is fed from a 15A circuit.
My speakers are as follows:
1.front mains are Precise Acoustic Monitor 10, 88dB eff.
2. center Infinity Beta 360
3. surround L, R Infinity IL-10.
I have played everything from Rock to Classical music and lots of movies etc.,up to -20 dB volume on my Yamaha RX-V2200 Reciever (used as a pre-amp). At that -20 dB level it so loud that I wish to go no higher on the volume!
It has never tripped the 15A breaker feading the amp.
I see no advantage in adding a 20A circuit. I don't think that any reasonable source will ever require All Channels Driven (ACD) simultaneously.
I support Genes' and Company ACD theory as fact.
In closing, I think the need for a 20A circuit would be a waste of my time and effort.