Currently on double click playback is stopped and the selected track starts. Unless i'm missing something this can't be changed. I would love the option to have tracks either played after the current track when selected or appended to the end of the queue.

Love your work. I think I've finally found my replacement for Media Monkey in Linux.

It can be changed by customizing your layout. Depending on your layout, you need to add a activate=queue option to the SongList or SongTree widget.
for example by changing a line like this :
VBSongList = HBSongList _SongList
into :
VBSongList = HBSongList _SongList(activate=queue)

the action can be play (the default), queue, playlist, addplay or insertplay
I'll add insertqueue (insert at the beginning of the queue) and a few others like remove, properties ... (suggestions welcome)
I'll probably add a way to change it via the gui in the future.

You might also be interested in the double middle-click : it enqueue the song (I may change that to a simple middle-click in the future). And btw, middle-click on a song in song menu entries enqueue the song too.

Solved, nice one. Thank you for your quick reply. Currently lack a middle click but will keep it mind for the future.
I think a gui way of doing is this is the way to go, not everyone will be confident customising layouts (and not everyone will bother to ask). Keep up the good work.