I consider it obscure since I consider myself fluent in English and I experience media for decades now, and never ever encountered the term transmedia. What you describe sounds like multimedia. Or a multimedial approach to market a franchise - which is quite normal.
What is not done, is making it depend on each other. People do not like that. If you have to read the comics to understand the movies, or rather if you have to read and watch both, but also have to experience the audio play to get the narrative, that's just bad storytelling to my understanding. What sometimes is done is complimentary things. I remember reading a backstory comic for the Portal game. It was only a few pages that would lead up to the start of the game.
It just has no relevance - so making a jam about it is perfetly fine. Just do not expect people to understand it by the term transmedia alone. They might think of the t in lgbt when reading transmedia. There is not even a wikipedia entry for the term. Oh, they do have a redirect to transmedia story telling, but that article has several markings of non relevancy, original research and such things. It seems to be a descriptive phrase and "transmedia" does not carry the meaning all by itself.
Actually, when I think about it, a video game itself might already fulfill the criteria of this "transmedia" thingy. You can show images, show videos, play sounds, show text and even combine it with user input.
As an example, there are these rpg games where you would find ingame books and those would have a story. Elder Scrolls games have this a lot.