Just to post an update here:
As discussed on the other thread by SnehaAgrawal-MSFT - DeviceManager.getMicrophones / getSpeakers doesn't return all devices (please continue your discussion there).
"Apologies for late response and issue you are facing here! As per recent update here this is known issue and team has recognized that there's a gap and some specific behavior can't be achieved. Team will be looking closer to this in upcoming sprints but nothing definite at this point of time. Having said that, I have reached out to you privately, so that we can assist you if its blocking you from integrating ACS."
Thanks for your patience and cooperation!