Is it possible to adjust the sub trim level while playing music in stereo mode? So far, I have not been able to do this. I can adjust it when it is in 5 channel stereo mode using the test button, enter x2, etc. on the remote, but when I try it in 2 channel stereo mode, it only toggles between "front left" and "front right" even though the sub is still receiving a signal. Since I play all my music in stereo, I would like to be able to adjust the sub while listening. Am I doing something wrong?