I have the same cabs and had the hardest time figuring out which jack on the back
is the input vs output. 2 parallel jacks with NO LABEL.
I think I figured it out but if anyone knows for sure please enlighten us
You could open it up and look, but probably the reason they aren't marked is because it doesn't
matter which jack you use.
In all likelyhood the jacks are paralleled
at the jack, like most PA cabinets.
Pop one open and check to be sure.