I'm 99.999% sure the tVox tour does not have midi.
Nonetheless, if you are looking to contact either Lydia or George (spelling?) the email address on Lydia's website - info {at} lydiakavina {dot} com works fine and they are very approachable people.
The only midi theremin I know of in production is the Jaycar Midi Theremin (http://www.jaycar.com.au/productView.asp?ID=KC5410) - it is very small and does not offer pitch-bend.
Both Wavefront Technologies (http://www.theremin.ws/midi.html) and theremin.co.uk (http://www.technomage.freeserve.co.uk/tmin.htm#mcv1a) offer rather pricey theremin to cv/midi converters.
My experience with the vocal pitch correction included in Apple's GarageBand application suggests that it works very well with theremins, but is too slow in software for practical use. A hardware pitch corrector might be a solution to your friend's problem, again price notwithstanding.
Alternatively - the analog CV path offers possibilities - there in the ePro of course, or the etherwave offers a simple mod for volume to CV and I have read that pitch to CV calls for nothing more complicated that a zero-counter module.