I have a different issue, but similar in scope, whereby everything sound fine, and coming through in stereo. But, when you switch the balance left to right, the sound mutes in only one channel when turned left, and then when turned right still has music coming from both channels. When in the middle it seems to sound just fine.
Where mine is a loaner (although brand new) while I wait for a 5.5 I am not going to stress about it, but figured I have a 'balance' problem with a 2.5 as well.