I didn't start this thread to figure out how to sail a Jeanneau 349, but if I didn't think it was too much load on those rings, I would think that extra gray line in the ring was a double ended mid boom mainsheet led back to the cockpit on both sides. And the rings are not adjustable to change the lead angle of the jib sheet.
There's a 349 on the dock next to mine, I'm definitely going to check it out next week.