No 2-axis pedal will ever match the many degrees of control that your mouth offers.
That said, here's a convincing Axe-Fx approach:
1. Amp, Cab, Formant, in that order.
2. Starting Vowel OOO, Mid Vowel AAA, End Vowel AAA - but I really didn't use it
Maybe it doesn't have quite the power of the real talkbox, but crank this over a cover band and I guarantee people will run to come looking for the tube.
It also helps when one learns the song. I didn't
Bravo!!!!!