Captivate 5 NeoSpeech - GUI editor for VTML behind text?

Question

Is there a GUI editor to embed VTML “behind” text?  It seems NeoSpeech is the TTS engine of choice for English (US anyway). 
Testing with Captivate 5, the generated audio is *almost* good enough for use as a narrator.  We have training “slides” where we voice over to enhance the experience.  We have been recording audio but keeping the same person working on this project is difficult.  I’d like to have a quality, reproducible source like TTS and the current implementation of NeoSpeech is about 95%. So, I’m thinking of planting VTML in the text but this makes the text awkward and the VTML is not for a casual user. 
Is there a way to develop a plug-in that would allow an app to get to the text, manage the VTML behind the scenes something like OOXML is to text editors?

Answer 1

I tested the "Loquendo" voices as Ashwin suggested. Mainly the British English one, Simon, as that can be somewhat compared to the US English. I think I like Paul from Neospeech better, but such a statement does not say much. Here are some more details:
I like the British sound of Simon, I really do. But as far as the natural flow of the sentence - it is not as fluent as Paul from Neospeech. With Simon, I hear that the sentence is combined from independent units - words; sometimes there is a little break in between them (more noticeable than we would naturally do). Paul's renderings sound more like a solid sentence. Also, with Simon, I hear some unnatural intonation shifts in a middle of a word. Not to say that Paul does not have them - but not as often (and the latest Paul from Neospeech's website has very little of them).
On the other side, I do not mean to say that I like everything from Neospeech. I do not like Kate - her intonation is sometimes very unnatural (to my ears). And while some say that the newest voice from Neospeech - Julie - is even better, I like it little less than Paul. True, Julie has a very nice delivery and some words she pronounces very clearly, but other parts she says indistinctly, causing me to wonder if she has an accent, or just lisps. Generally, I prefer male voice over the female one when it comes to computer voices, as the female voices - being in  higher frequencies, get more of the s sound. (Perhaps a de-esser could be built-in to the future version of Captivate to improve the voices :-).
  If I were to compare the English speaking voices, my list of preferences would be: 1. Paul, 2. Julie (this one is not in Captivate), 3. Simon + Kate. But remember, my ears are different than yours, so this all is just about what I like...  Martin P.