The first step is to convert the sounds to one of the supported formats. I recommend WAV or FLAC. Then you can Import
it. You'll get an expression of the form
Sound[SampledSoundList[{leftChannel, rightChannel}, sampleRate]]
where rightChannel
and leftChannel
are numerical lists of amplitudes.
Generally, if you want to hear the sound from just the left speaker, you need to create an all-zero amplitude list of the same length for the right channel too.
For example, after extracting data from the above expression, you can re-create it as
Sound[SampledSoundList[{leftChannel, 0*rightChannel}, sampleRate]]
to mute the right channel.