It depends on how the sound card sends the signal. RadioBOSS determines how many channels are there in the input, and if it's mono, it copies it to both right and level channels. If there are more than 2 channels, they are downmixed to stereo. It appears that your sound card sends two channels, with audio in the left channel and silence in the right, and that is what RadioBOSS outputs. You should open sound card control panel and switch it to mono.
