Having just carried out a quick experiment it appears you can't export a track that's been sent to WaveEditor from within Power Director. If you run WaveEditor as a stand-alone and import a sound file you can then edit and Save As a new file.
So it looks like you can't extract audio from your video by this method. There is another way, however. You can use the Produce function to generate an audio-only file from the video as a WMA, WAV or MP4.
Regards,
Mike
Home-build system:
Intel Core i5 Quad Core 3.3GHz, 2 x 4GB DDR3 1333MHz,
Asus Nvidia GT440 1GB, 2 x Western Digital WD10EARS 1TB, 1 x Seagate ST1000DM010 1TB,
Windows 7 Prof 64-bit, PD 9 Ultra 64, PD 13 Ultimate 64