I flew CX F HKG-SYD and was able to use the QF/BA lounge at HKG based on class of service alone.
The only thing is that upon entering the QF/BA lounge, the lounge agent said "please be aware that we will not be announcing boarding for CX flights so you will need to keep track of the time".
When I flew CX F JFK-YVR, I was able to use the AA Admirals Club at JFK (after arriving from a US domestic flight). Same thing, the agent just made it clear that they "will not be announcing boarding".