Well, not exactly what you're asking for - but a bit more streamline is this:

1. go to Tracks in Library
2. click the ... icon for the track you want to add
3. choose Add to Playlist
4. choose Playlist (or make new one)

This at least avoids having to move back and forth between Tracks and Playlist sections.

when I do that it brings me to the playlist I just added the track to.  

Are you on the most current firmware (1.10.78)?

I am 

Hi James,

I think you're asking how to edit a playlist not just add a track. Follow these steps:

• Select Library on the bottom menu
• Select the playlist you want to add tracks to
• Select the edit icon on the top right
• The first page allows you to re-order tracks in the playlist
• Select add tracks near the top, just under the playlist name.
• From here you can add and remove tracks at will by hitting plus or minus next to the track. When you add a track it's added to the end of the playlist. 
• Hit done on the top right to go back to the first page to re-arrange your tracks. 
• Hit save on the top right when you're happy with your playlist.

There is not currently a way to sort your playlists. I'll note this request.

Thanks!