Hey there, it all depends on your skill with soldering and electronics. Keep in mind that if you do it on your own, you void the warranty so it's probably best if you have UltraSabers do it. Just contact customer service, they'll give you direction
Adding sound to an Emerald led driven lightsaber will be a challenge. You'd need to cut some wiring that go from the card to the battery holder and add some too. This diagram will give you an idea:
From my 2 Emerald & Obsidian v3 lightsabers I have, US uses a jumper connection between the 2 boards, then wires in the LED module, switch, battery holder and speaker.