Actually 7 using 2 ,4 & 8 Ω speakers. And 6 using just 4 & 8 Ω speakers
A & B and A & C is parallel
B & C is series
1. One set of 4Ω speakers connected to either A ,B or C. ( 3 )
2. Two sets of 8 Ω speakers connected to A and B or A and C. ( 2 )
3. One set of 8 Ω speakers connected to A and two sets of 4Ω speakers connected to B and C. ( 1 )
4 Two sets of 2Ω speakers connected to B and C. ( 1 )
Same applies to any M and MX Yamaha amplifiers that have A,B & C binding posts.