Technically, its not quite a talk box (sealed speaker with output via tube to the player's mouth). Rey's wife is offstage modulating the sound with a carbon throat microphone.
Alvino Rey was also instrumental in the design of the first electric guitar, Gibson's ES-150 of 1936.
Technicalyit's not "two handed tapping" in the guitar sense, since this isn't a fretted instrument so you can't tap in the guitar sense.
"carbon throat microphone" is a mistake in the Wikipedia entry, the Sonovox was actually a small SPEAKER (or two) attached to the throat. Here's a video that actually shows the device itself: