You bridge the two channels for the subs then run subs 2 ohms. Other 2 channels can run 2 of the 6 1/2 on each of them. Not a problem sense amp is 2ohm stable. You will have to wire speakers a little different. The 2 6 1/2 that are at the back of boat will need to be wired to one output channel. The 2 6 1/2 in front of boat need to go to other output channel. You might have to use the left to right fade in order to fade front to rear. The 2 channels you are using for your 6 1/2 are true front output channels they will fade left to right. Your rewire job will allow them to be used for front to rear. I hope I did not lose you. The amp you have will do what you would like to.