Same as on the hd500, it just can't happen. There missing a major trick here. They have made it far to fancy. All the effect needs is to be able to select start and end vowels and the way in which you control it. Who on goods earth would control a talk box exactly at tempo???? Come on line6
I don't have it in front of me, but I think the v-tron effect has a sensitivity parameter that works pretty well for Man in the Box. Set it right and you can accentuate the vowel sounds with how hard you pick.
For this reason i gave up using talkbox effect on hd500. I am getting usefull results with narrow Q filter and control the frequency with exp pedal. It is kind of custom wah but sounds ok for what I need it for.