This was my solution cause I was having the same problem.
1. Use perian to just save a .mov of the mkv (wrapped not transcoded)
2. Use that .mov and export (transcode) using quicktime to prores and force fps to 23.98
3. That then shows up in final cut as 10fps and when i drop into sequence audio is off
4. Make new sequence with what i want as my settings
5. Drop step 1 file (the wrap) into the sequence (should need rendering)
6. Drop the transcoded mov into that same sequence
7. Delete wrapped mov from sequence then render the transcoded one
thats the only way I got to bypass the 10fps issue