I can't really advise you on the use of the Lorann oils, since most of them are artificial flavors, I avoid them. The Navan is so expensive and so delicious that I wouldn't do anything to it.
I just did the grand marnier version for a birthday cake for the food writer of the Raleigh paper. Her friend throwing the parrty sent me his email -
"Katrina - the consensus hands down was that your cake was the best of the best - thanks so much for a beautiful end to our meal - we all ate every drop of our slices - and the birthday girl's husband ate the rest before the dawn came after she brought it home -
I really appreciate all of your effort as did the other crazy wild women who attended our soiree........many, many thanks to you! You obviously are an award winning pastry chef!"
While I always encourage people to make recipes their own, try this one as written first. It really doesn't need anything.