I just shot a piece with the FX6 and FX9 and wanted to start editing today. I thought I could simply create proxies from my 4k material and dig in. Not the case. I'm using Adobe Premiere and there seems to be a bug where the proxy export creates proxies that mess up the 8 channels of Sony audio (btw, I need to learn how to shoot so it's just 4 channels).
I cannot find a workaround besides RE-ENCODING all the footage. That's terrible. If anyone has another solution let me know.
But this helpful YT video from this past August says this is the way to do it - I'm on Windows, but following this video, I guess I'll just transcode everything to Apple ProRes 422 and create proxies from those files. My first test worked. The audio was fine!