Hi Bill,
By same leg, I mean same buss and same phase. There are two hot buss bars inside the service panel, each one carries 120V in opposite phase.
A double pole circuit breaker takes up two breaker positions in the panel and connects to both busses, adding together the two legs, giving you 240V on the line.
A single pole breaker only connects to one hot buss, only takes one (or half) position and only provides 120V service. A single pole breaker can use either buss, but not both. Since the two busses are opposite phase, two separate 120V lines could be either in phase or opposite phase depending on the panel position of the circuit breakers. The two opposite phases should not be mixed together in the audio system. Choose breaker positions so that both circuits use the same buss and have the same phase.
Breakers alternate phase through vertical positions in the service panel, while breakers on the same horizontal row are the same phase.