Welcome to Flyertalk and the JAL forum.

I don't think you need to go into to the multi city search to put an itinerary together. If I search in the standard booking flow, in November I get a PY connection for 4.2K AUD offered. I leave you to judge the price level for Sydney Paris in PY, as I don't know the market.

Since the standard connection via HND leaves a 17 hour stop in Haneda, you might want to see if you can do a JL52 JL41 and then BA to Paris. SYD HND LHR CDG, as the connection works better, returning is fine for CDG HND SYD.