if you’re talking about the positions of the keyframes into your timeline, you can simply ALT drag your KF after you selected them. You should be able to move them evenly.
Maybe you should re-render your audio file into a more specific format before exporting your project. I’m thinking of uncompressed format such as AIFF or WAVE.
This is actually part of my workflow, I ingest via FCP 7 and then copy the files into FCP X. Just find your capture scratch from FCP 7 and drag the files you want into a FCP X event and they will copy over. 🙂