All I can add to this is: Whatever exercise you do, always keep your shoulders back and down. This creates the most room inside the shoulder, and its also a strong position for it. Imagine pinching a tennisball between your shoulders.
Another thing I was told regarding my impingement was "Its ok if it hurts a little bit while you're doing the lift, but it must NEVER hurt afterwards"
I havent had any surgery, just a cortisone shot (impingement), but its been almost a year now, and I'm still not 100% ok. Flys, benchpress, incline bench, shoulderpress, lat-raises etc, all hurt to some degree.
I hope you do better
Good Luck!
/Maf