Great build!! As for sound, I would think the standard Obsidian board would work just fine, as it already fits the MHS parts, and has plenty of customizability for sound.
I actually do not have any sabers with Obsidian. Would it work using a switch as a trigger? Obviously, I would just want sound to come out when the trigger is pulled, not all of the time. I have no experience with Obsidian so any hits would be great.