Well, that sucks. Lol.
I think it'll just be a case of strafing between the two pillars and firing away.
Autumn doesn't take many hits, but his guards are heavily armored.
You might want to kill him, take his Plasma Pistol, and fight off the guards with that.
However, if you're actually in the room prior to the conversation that Autumn has with you, you'll be able to speech challenge him into giving up and commanding his guards to stand down.
Just re-load the game after each failure of the challenge until you win.