With the general idea of getting the most value for a xONE(4-5-6) purchased in SE Asia here are my general strategies ex CMB. No apologies for the fact that a PER location makes this less expensive.

East bound:
To hold the ticket for later use - one stop in SE Asia - SIN-PER-SIN as an extra ticket (QF V class) - inexpensive considering QFs prices exAustralia. Then SIN-(HKG/NRT)- North America. You could use both of the SE Asia stopovers but then you would need to go back to CMB without a stopover at the end. Also the LCCs may actually have better schedules exSIN to some of the tourist spots (Siem Reap and Borneo come to mind) and the flights are short (1 to 2 hours). At the end of the xONEx route Europe to Australia with a direct flight or a single plane change. Use the SWP segments then [SWP]-HKG-CMB.

Westbound:
No issues except you must use a North America -> [SWP] routing. then [SWP]-SE Asia.

Any thoughts on stopover points in Europe where EASY and CHEAP connections to interesting tourist spots - using tickets outside of the xONEx? BUD? PRG? IST?

Happy wandering

Fred