1. Check that the panning is correct in the Studio One Master Bus, that when you pan left the meters go left and vice versa.
2. Make sure you aren't using something flipping the panning like Dual Pan.
3. Make sure the FSM outputs are correctly connected, that the left output is going to the left speaker, etc.
4. If using the VSL mixer, check it to be sure panning isn't flipped in there somehow.
Run these panning tests using a Test Tone plugin on a mono audio channel. The panning is flipped or reversed somewhere in your system, you just to need to test it to figure out where it's flipped. (of course, make sure your phones marked L/R are actually Left and Right.)