This has bothered me since I bought VoxATC, things like pronouncing wind "wynd" and Qantas "kantis" and I could never find a solution until recently... And it's obvious and simple!
VoxATC uses the microsoft voice recognition engine so I went into the control panel/Ease of access/start speech recognition. Then activate speech recognition by clicking the microphone icon and say "open speech dictionary" From there, simply add any words that VoxATC has been mis-pronouncing into the dictionary and make sure you record a sample of how you want the word to be pronounced at the end. For unusual words (like Qantas) I had to save the word both in lower case and capitals to ensure it always is pronounced correctly. You can test that it has worked by typing the words I no a txt file and have Narrator read it back.
Hope this helps as it was driving me crazy for a while there!