I am trying to build an application for intercepting the audio from player before it reaches the real sound card and redirect the audio stream to RDP virtual channel so that
The only reliable way of doing this would be to write your own audio device driver, which is not a trivial undertaking.
A compromise solution would be attempt to write an application that records the output to the soundcard. In Vista and above you can do this using WASAPI to do loopback recording. In XP, you have to hope that your soundcard manufacturer included a "What U Hear" (sic) record source with their driver. See this question for more info.