4 channel surround from PC w/ active spkrs?

A question for a friend who likes good sound from his PC for games and movies, in a compact nearfield setup...

PC games have a 5.1 soundtrack that is sent to 6 discrete channels (afaik).

The Realtek sound cards in most PC's have a setting for 4 CH (four speakers).

My friend is hoping the Realtek driver will somehow downmix the 5.1 to 4.0, so he can feed those analog outputs to his KRK front pair and M-Audio rear pair active (amplified) speakers.

Has anyone tried this? Will the games' center channel be routed to the Front L/R, or will the center channel simply disappear, lost in translation?

I tried to talk him into trying stereo, since he's sitting so close to the speakers, but he really wants rears. The PC games don't give you a 4 channel or Quad option. Just 5.1 or stereo.

Any info would be much appreciated.