Unfortunately, browsers only support sound cards’ first two channels at the moment.
If you put your microphone when using a sound card with various channels on another channel, WebRTC won’t work.
But there is a trick when using Windows. You can install a so-called virtual sound card. A suitable software for this is called Virtual Audio Cable. With the software’s help, the existing sound card (your sound card with various channels) can be transformed into a virtual stereo sound card which can now interact with the browser as well.