I have this problem with the IGMM Asia replays, and now I'm having the same problem with the Star Series (tried Na'vi vs Empire). I selected the audio channel of Sheever, and Tulex was her co-commentator, but I couldn't hear him. Actually, he has his own separate audio channel, but in this case I couldn't hear him in his channel. In IGMM both audios are working, but alternated (when one commentator speak, the other stop talking).