Here’s how I’ve been doing it, when NECESSARY, otherwise I keep the edit in 7.
I media manage the sequence. As a new project. I usually name it “Project Name – Sequence MM 20140723”
Then I open that project (which is really just a sequence) and XML that.
It has been very time consuming, by the way. And it hasn’t been perfect because some editing techniques (not to mention plug-ins) simply don’t work the way they did in 7.
Bottom line: I will continue to use 7 for the next decade simply because of the amount of projects sitting here. I keep them all on an Xraid with a 10.6.8 system.
Note also try removing every single effect and setting on the audio tracks. It could be the XML just doesn’t recognize them as viable audio. Additionally, you will need to re-render everything back in PP, so any audio that has been rendered, and FCP is looking at the render file as the file, means it isn’t getting XML’d. (Make sense?) — hence the media management step.