I am looking for some clarity in the Helix Owner's Manual,
1. What is a "mono play-back system" ?
2. Why "connect only the left/mono XLR jack?
Below is a link to the Helix user manual regarding this topic.
25. XLR OUTUse balanced XLR cables to connect to your studio gear or the house mixer, PA or FRFR speaker(s) when playing live. When using a mono play-back system, connect only the LEFT/MONO XLR jack.
This should be an informative post for, (i would guess 1,000's of people? If not more), and expect to expand on the topic.