I Have the same problem, I can get them to work by pressing the Vol Down key for 3-4 seconds, but then the inline control doesn't work....
It seems to be a fairly common problem with the Xperia Z2, I't not just the piston, my Klipsch s4a don't work either, and I brought the piston just to replace them and..... well...:crying:
Here is a similar thread, and on Sony's forums the standard answer seems to be "It's not our problem, try asking the manufacturer"..... it seems we have to wait until enough people start complaining and Sony decides to patch the phone....