* This may take some time; progress is indicated by emission of the Progress signal.
* @param files Pathnames of sound files, in the order Left, Right, Centre, Lfe (sub), Left surround, Right surround.
* @param directory Directory in which to create MXF file.
* This may take some time; progress is indicated by emission of the Progress signal.
* @param files Pathnames of sound files, in the order Left, Right, Centre, Lfe (sub), Left surround, Right surround.
* @param directory Directory in which to create MXF file.