Thanks.
So far, to get over this problem, I am not using the zoom within megazine, only using megazine for the page flipping. Instead, I have created my own zoom functionality by changing the scaleX and scaleY of the megazine instance on stage.
But this workaround is causing me huge performance problems as it relies on having each page as a hi res image (about 15 mb each).
So... if I could use Megazine for the zoom, particularly the adaptive zoom, my life would be made much easier. I just need to be able to create that smooth tween between the two zoom levels...