Something along those lines (thanks) seems to be what one has to do.
Method:-
1 - Edit video on video track in the usual way. When you've trimmed the clips as required (and to crossfade the audio, you must trim the clips at least a bit at each end) then ....
2 - Go through each clip and right-click-select "Split Audio" which sends the audio down to the Voice Track without creating another file. [Comment - it's a real pain to have to do this clip by clip, rather than selecting all of them and doing it in one go, but the option isn't shown if more than one clip is selected. Also, clicking the confirmation box every time seems quite unnecessary and a further obstacle].
3 - Drag each alternate clip down to the music track. Do this carefully without moving it sideways else sync to the video will be lost. [Comment - there seems to be no key combo for doing a vertical move without going sideways - I would have expected something like ctrl/drag to do this.]
4 - Now you can drag the right edge of the first clip's audio beyond the right edge of the first clip's video. Do the same for the left edge of the second clip's audo. Using the volume line or the mixer fade out the first clip's audio and fade in the second clip's audio at the point where they overlap. Voila, butt join video with smooth audio transition, just like almost all edits on the TV.
5 - With luck, if you do need to adjust your video edits, the audio edits will more or less adjust to compensate, though you may need to redo the fades at the point of change. I'd recommend saving your project to several version files (eg at the point where you finish video editing, and the point where you finish audio editing before doing anything else, etc)
BUT - good grief, that's a long winded method compared with simply dropping an audio-only transition between two clips. I really do hope Cyberlink will add this badly needed but quite simple thing before too long.