I have my default Track setting as Midi as I prefer the ability to contol the Wave inputs. If the Merged File is Imported and the Track type is Midi or Audio-Mono then you are asked to choose either Stereo or Mono and if the latter then you a further option to split the Mono Wave into two tracks. If your Track Type is set for Stereo then no options are provided. I believe that the default setting for Track Type is Stereo and would be better set to Midi.