You should be able to set the Recording Levels for your Microphone and your general output of applications (StereoMix/WhatYouHear/Speakers) separately, in Windows or your software that comes with your sound adapter (motherboard drivers, installable drivers from your soundcard manufacturer). In either case, you should be able to set the volumes differently and test them out until you get it just how you like.
I don't know about Cyberlink's app, but you may have to look around for a video editing program that will handle them as two separate audio tracks/files, then you can also adjust the sound in the editor, if you want to. I prefer Sony's Vegas (you can get a less expensive version of the product), but I think most of the non-free video editors out there will handle two audio tracks.
You could also take the two WAV files and import them into something like Audacity (which is free) or any audio editor you prefer, and adjust the volumes before mixing into one audio track. Then you can import your finished audio track into whatever video editor you prefer (like your Power Director). You may have to contact Cyberlink or check out their site to see exactly how it would prefer to handle the tracks.
Good luck with it!
("Hope That Helps!") ~ Troy