Ciao Janita, I happen to mention fixatives mentioning this to be an attributed quality of some essences but I never wrote about them in my texts on perfumery or ever teach about them in my courses. To my perfumery students I read the words of Guy Robert:
“I hate and find stupid that theory of “fixateurs”.
We all know these many little songs we are hearing anywhere and forgetting almost immediately, but, from time to time, one of these songs sticks to our ear and we go on whistling it the whole day … I can assure you the author of these successful songs do not use any “fixatives ingredients” to get that result …”
it is a very interesting lecture at: //www.bsp.org.uk/newsarc/biogenesis.html
Guy Robert is the composer of Amouage and Madame Rochas among many famous others.
As a blender, rose wood is the one I use most, as a potentiator Ambergris is remarkable.
I do not know in which perfume Hyraceum is used, we should ask Guy Robert.
All I know is that no good perfume can be without naturals, although I cannot smell them covered as they are by synthetics, and the use natural has drastically decreased in the mass products of the last years.

AbdesSalaam Attar
Compositore Profumiere