FFMPEG - Creating multiple copies of a video with different audio channels. Can't hear channel 4

I'm working on a project where I need to have 6 copies of a video, where each copy only plays one audio channel. The original video has only 2 channel, with the same audio on each channel. First I had to copy one of the channels into the other 4 missing channels. I'm new to ffmpeg, I did some research and I used this command:

ffmpeg -i input.mp4 -map_channel 0.1.0 -map_channel 0.1.0 -map_channel 0.1.0 -map_channel 0.1.0 -map_channel 0.1.0 -map_channel 0.1.0 -c:v copy output.mp4

That helped to turn the video into a 6 channels one. Then, I revised the command for each channel:

ffmpeg -i input.mp4 -map_channel 0.1.0 -map_channel -1 -map_channel -1 -map_channel -1 -map_channel -1 -map_channel -1 -c:v copy output_channel1.mp4

ffmpeg -i input.mp4 -map_channel -1 -map_channel 0.1.0 -map_channel -1 -map_channel -1 -map_channel -1 -map_channel -1 -c:v copy output_channel2.mp4

and so on.

All the videos worked perfectly on their own channels, but channel 4, in which I can only hear some low noise. I read channel 4 is used for low frequency audio in 5.1 configuration, which might be the problem. I tried specifying the channel layout to 6.0, increasing the volume, disabling guess_layout_max, but nothing worked. As I said, I'm new to ffmpeg, and probably there is a much better way to do it. I'd appreciate if someone here could help me. Thanks!