Thanks for the information, everyone. I use Muse by choice, because it does allow you to choose the line breaks, and the note and line spacing adjustments you prefer. It also produces reasonable tablature, for mandolin, guitar, and other stringed instruments,in the tuning of your choice. It's shareware, and it is powerful---but the menu system is complex. I do prefer to use ABCmus for playback though.
Still, it's what I've used for 2 years, over any other I've tried...despite it's drawbacks.