notsofatso and nsflive (and maybe some other players) allow you to set arbitrary panning for each channel, including expansion chips. panpots are set by default, so all you have to do is a play an nsf in one of those players and you should have stereo output. however, understand that neither the 2a03 or any of the expansion chips support stereo control natively, so there's no way you can get panning at authoring level (curiously unlike the gameboy, which does indeed have pan control.)