The speakers I'm using are Klispch 5.1 indoor and Bose 151 outdoor. Any help you could offer would be appreciated. Thank you.
You can't run A & B speakers together. The impedance is too low, and demanding more current from your receiver than it can supply. If you continue to do this you will destroy the receiver's amps. If you want to run both sets of speakers together, then you need to run a separate amp from zone two to drive the Bose speakers.
When you use A & B outputs together, it just couples the speakers together and it is the same thing as connecting the wires from the two speakers together and just using one set of speaker terminals.
Receivers have all the amps in one case and are usually limited in their ability to provide large currents over time. However make sure you check your speaker wiring and that you have no whisker shorts at the receiver or speaker terminals.
You did not state which 5.1 system you have. If it is
this one for instance, Klipsch rate it at 8 ohm nominal. However, because of the driver layout, it has to be 4 ohm below 400 Hz, and that region will consume 2/3 of the amp power at least. Manufactuers are very loose (lie) about their impedance specifications.
If everything is connected right, and you have speakers with more than one bass/mid per speaker, and you can't play at your desired listening level, then you will need to add external amplification, with higher current delivery capabilities.
