I answer myself
I made a test and I'm able to achieve that result by using the "SetStereoVolume" command of the AudioTrack library.
By using the
at.SetStereoVolume(at.GetMaxVolume,at.GetMinVolume)
I set the volume of the right channel to 0 and the audio is sent only to the left channel.
Vice versa with
at.SetStereoVolume(at.GetMinVolume,at.GetMaxVolume)
I set the volume of the left channel to 0 and the audio is sent only to the right channel.
I hope this may be useful in the future.
Andrea