Thanks for the help. Minor correction to serfty that AA fly from both ORD and DFW to ROC. The reason not to do JFK is that all but three notoriously delayed DL Connection flights from JFK to ROC are operated by B6, which is itself hard to interline to, being an LCC, and you don't want to take QF107 to JFK without misconnection protection!

I decided to solve the problem by reorganizing my trip and making this part a simple US-Australia return, and also by accepting a later return to ROC. I'll do the RTW another time. The QF Aussie Airpass is so cheap that if you're prepared to fly in Y, it's an excellent deal (USD 1315 all-in for LAX-SYD-CBR-MEL-LST-MEL-SYD-LAX, all on QF, books in Q which isn't mileage-earning on AA, but I can wake up my dormant QF account for that price, and plenty of availability.)