Question: A while back I was wondering why my dvd was so quiet on my computer then solved it by chosing the 2.0 track instead of the 5.1 track.

But now I have a DVD which only has 5.1, how can I watch it without losing the other channels?

If it helps, I'm using Media Player Classic.

Answer: 
Use the 5.1 track on the dvd, then set the output in the sound driver to stereo. it should mux the front and rear channels together in hardware. if it doesn't get a better soundcard
If you use VLC there is quite a few audio tweaks you can do, but in the standard Audio menu you can choose between 5.1, 2 front 2 rear, stereo and mono.

I only had a quick look around the preferences so there might be something even better among the many settings. To get to the cool/advanced menus be sure to click the `All` radio-button indicated in the picture.

![alt text](https://i.stack.imgur.com/9j4M5.jpg)