LiveView Zoom is a misleading name, but it's the one in the documentation : when in LiveView mode, you can enlarge a zone of the LiveView picture x5 or x10, to perfect your focus.
About what worked, and what didn't, I think it was really just a problem of how we passed some variable to the sdk function. You may have seen that in the end, I didn't use the function and data type you created for the occasion. My success here is more due to luck in trial and error than anything else.
I hope we found le liveview memorystream solution soon, it's the only thing that I'm really missing now (apart from some code cleaning).