This is a widget for the Ace3 Config library. To use it set the "dialogControl" of your config to "Eliote-LSMSound":
sound = { type = "select", name = "Select a sound", values = LibStub("LibSharedMedia-3.0"):List("sound"), set = function(info, val) print(info.option.values[val]) end, get = function(info) end, dialogControl = "Eliote-LSMSound" }