But in a movie format, you'd need a horrendous amount of voice-over
I don't think so. Most things are pretty self-evident, I think. Like you can see a tech adept and go "Whoa, this guy probably loves machines because he's more machine than man now".
Other little things aren't super important to know. If someone gets shot up with frenzon, for example, the movie wouldn't have to tell us what frenzon is and how it works. Just have a chemical injector show and the guy go nuts and murder things.
The only tricky thing you'd have, I think, would be the political institutions, some of the Xeno culture (but you can gloss over that), and maybe the nature of psychic powers and the warp.
Getting all the nuanced information in a movie is hard, but getting the point across probably not so much.