I agree you sound card onboard will likely be your quality limitation. I mis read about your bit depth question as bit rate. You might need external AD/DA audio input for the higher bit depth. A device used to plug a guitar or other sound source that is analog and is converted to digital via it's sound card and then fed into recording software might help. That would take your onboard sound card out of the picture. You will have to see if you software allows choosing the audio input.
For software I use Reaper. It is free to try for 30 days. It accepts onboard and external input.
http://www.reaper.fm
http://www.sweetwater.com/insync/aud...-buying-guide/