Darkhorse have you bypassed the DI and is the output from your adapter lead direct to pa ok if so, does the DI have any phase reversal switches on it that might be engaged , if it appears to be the DI box as it has no reversal phase switches it is possible that it has been wired incorrectly inside the unit , take it back and try another DI unit otherwise open it up and find the incorrect wiring and fix it, I had an AirTurn foot pedal that someone wired incorrectly and the wrong switch was activating a wrong action so I just fixed it instead of going through the pain or returning it.
If it’s the headphone adapter, just get another one preferably an apple one or a well known brand.
Good luck