I have a customer that has multiple IPO 406 units, all at Rel 4.1 (15). One of the units has multiple DS ports that are bad and was wondering if he could just have me swap out the unit. I have a 406 on hand that is at Rel 4.2 (14). Will this be compatible with the 4.1 (15) units? I'm hoping so, as I don't think I have a copy of 4.1 (15) firmware around.