It sounds like it is summed to me but there is very little bass information that is panned on just one channel. Try it and see.
connecting subwoofer to parasound via loop output on A21+ / A23+ ?
Can anybody advise if the signal to the sub is summed, or do I need to connect both outputs to my sub?
their manual shows the following;
Loop Output Jacks
These jacks enable the incoming audio signal to pass along or “daisy chain” from the Left and Right
Input jacks to an additional amplifier or powered subwoofe