@rraud I am on Vegas Edit 16 and all the audio shows on the left channel only. The Tascam DR-60 MK II seems to have complications. I have a shotgun mic on mono for XLR input line one and on channel 3/4 had the stereo input from the lav mic. (Line two is an XLR port for another mono signal). I am not sure if the unit can accept mixed signals.
Another option; In VP's "Options> Preferences> General", there is a setting to import stereo files as dual mono. This will give your two 'separate' mono tracks on the timeline, instead of a two-channel stereo track, you could just remove the track you do not want or mix them separately.. if for instance, a boom mic is on channel-1 and a lav on channel-2. Assuming the DR-60 tracks 1 & 2 are an interleaved stereo file, which I believe it is, Tracks 3/4 and 5/6 would import as dual mono as well for total of six mono tracks.