You can book to SJU pretty easily on the QF website. You can use the multicity tool if you want to factor in stopovers along the way.
If you want to attempt a higher degree of difficulty, you could book your trans Pacific and your domestic US flights separately and take advantage of the AA discounted first class or business class fares for the extra SC earn for not much more than a Y fare. I wouldn't recommend this for a novice. If you attempt it, the main traps are that you won't be able to check bags all the way to your final destination so you have to allow plenty of time for rechecking bags between QF and AA sectors, and if there are delays on one airline the other airline will not necessarily help you out if you miss a connection. Also sometimes if you book on the AA website it does not ticket easily so you have to ring up to get it ticketed.
Another tip for flying in the US is do not lock your suitcases. Even if it is supposedly a TSA-friendly lock the TSA will just hack through them and damage them. Obviously this means don't pack anything you couldn't bear to lose in your suitcase!
Have a great cruise - please post in the cruise thread