Hi!
I am wondering how many channels by default does foobar support, and
why the "Convert 5.1 to stereo" option in DSP manager can't be configued even if it appears under the column of Active DSP? I don't have a 5.1 stereo, but a 2.1 stereo connected to my PC, and so I am thinking if the audio output will be of better quality if I can have "Convert 5.1 to stereo" configured.

"Convert 5.1 to stereo" has no configuration options. It does exactly (and only) what its name says.

Thanks, foosion!
One more question here,
Have you ever installed Channel mixer for your foobar? how do you feel it?
Did it make the audio output feel better?

I don't use any fancy DSP effects. In fact, the only DSP I normally use is the advanced limiter.