Avios would be a MUCH better option on a separate ticket (9K Avios vs. more than double the same number of AS miles). Note that separate tickets means CX will not be required to rebook if JL gets you in late to miss a flight, so a stopover would be a good way to deal with that.
Also, AS official policy (per the CX wiki) is CX stopover is only allowed in HKG, TPE would not be allowed. I’ve been denied similar stopovers in CX fifth freedom cities (BKK). If you feel like playing the HUCA gane to find a phone agent who will ignore the rules I guess you can.