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Settings-apps-all-sound enhancements,force stop and clear data.Restart.
Even if you scroll to all? It should be there.
Strange,it can be found in my Z1 and I am sure in most of Xperias.In this case,boot in safe mode and check if the same occurs:
http://talk.sonymobile.com/t5/FAQ/How-to-boot-your-phone-into-safe-mode/m-p/348008
Have you pressed the power button and after that tapped longer on turn off? you should get a message to restart in safe mode.
Of course it works.