Thus far I have always managed to get my AVCHD files into MC6 either by direct import or by transcoding when it refused to cooperate with the import. Once ingested, all is well, but it can be a lengthy / trial and error process, particularly with long files.
I have never yet tried a project using only AMA linking because I am nervous that once complete the export could fail in the same way that import often does and transcode occasionally can.