How to mix 7 mono channels to stereo?

Yes.

I just need instructions on how to mix front_left, back_left, side_left and front_center to left channel, and front_right, back_right, side_right, and front_center to right channel.

What are Pan settings for the front_center channel?

Is the front_center channel mixed two times (once to the left, and once to the right), or just one?

Should I decrease volume of certain channels?