You could also take CX / connect in HKG.

CX138 SYD (21:55) to HKG (05:25+1) connects well with CX723 HKG (08:50) to KUL (12:30). The return also connects pretty well (CX722--CX111 or CX724--CX101). Yes it's a longer flight, but without having looked, I would be surprised if it really took much more overall time than the SYD-PER-SIN-KUL option that was mentioned.