Wow that will be expensive. But I really like the idea of turning the war glaive into a double blade saber. But I was trying to go on a budget and go for the phantasm. But was wanting to know if I can make the phantasm have sound if I chose to later on? Or is it even possible with the cheaper model sabers? If not or if its too much work ill just go with my dream saber. The war glaive. And slowly turn it into a double blade saber.
Here's the problem there: the Phantasm is a great weapon, but see the sound from a saber comes out holes in the pommel typically. This is why the coupler for the sound sabers is vented, so the sound will be able to be heard still. The Phantasm coupler is just a simple male-male connector, and gives no method for the sound to escape even if sound is installed.
One option, keep in mind I'm very new to saberbuilding so this is speculation, is to drill some small holes in the side of the sabers near the bottom (below the speaker, when you install it) and use Econo sound - this is a soundboard taken from the $20 Obi Wan Kenobi light up saber toys.
My advice is talk to Ultra, he does the custom work around here. He's super busy right now I'm sure, but maybe when he gets some more time he can help you with this problem.