SYD-JFK
JFK-MIA
MIA-BOS
BOS-DFW
DFW-LAX
LAX-YVR (seperate on AS)
YVR-JFK Just check that CX have traffic rights on this route for your ticket.
JFK-LHR if you do not have to do EDI before CDG then I would suggest taking AA on the JFK to CDG and then you could skip a coupon from the country pass later. Don't know your priority here and if you even want to stop in London at this point in your trip.
LHR-EDI (seperate on oneworld country pass) see comments on other posting.
EDI-CDG (seperate on oneworld country pass)
CDG-LHR (seperate on oneworld country pass)
LHR-MXP Why MXP and not LIN, MXP is a pain to travel to and from if you are going to Milan city. Do not arrive late at night at MXP it will take you hours to get into the city on the bus as the trains have stopped running etc... (particularly the BA that lands around 2200) If you do need a good hotel just off the airport at MXP then the Villa Malpensa is good but can be expensive. The shuttle can stop running around the 2200 time and so you have to take a taxi round the corner, or walk for 15 minutes along the roads as I do.
MXP-LHR oh yes, watch out for the fog...
LHR-DXB
DXB-LHR option of day and night flights, decide to sleep on board or hotel.
LHR-SIN any reason for not doing LHR to HKG direct to save the next coupon?
SIN-HKG
HKG-TPE
TPE-NRT
NRT-HKG
HKG-AKL good for the 5000 mile requirements
AKL-MEL
MEL-PER
PER-SYD

I might just consider going to Sri Lanka on a cheap ticket and buying a CX issued AONE4 for the same price as your DONE4 from SYD.