Firstly, thanks for contributing to this project!
Now, I understand everything you're trying to say even without the pics, but there are two reasons why I would not be dealing with multiple selections:
(1) At the back end, it's very difficult to change the list-boxes (the boxes with the item names) to behave as multiple selection boxes.
Although there are some ways to do it, more importantly I find it (2) redundant. You see, the list-boxes are in an alphabetical order, and as a fan of music, I wouldn't be basing my selection of the next song on the order of the alphabet.
The goods news: in your last picture to the right it shows how you'd want to re-arrange the order of the list.
If you wish, I could create two more buttons -- up and down -- to allow you to move the selected item from the queue list (on the right).
When moved up the list, it'd be played sooner (after the tracks above it), and when moved down, it'd be played later.
To do a hands on trial of what I described in the last paragraph, do the following:
- Open Winamp
- Load some songs into the playlist
- Press 'J' on the keyboard
- Enqueue a few songs -- select from the list and press 'Alt+Q'
- Press the big, horizontal button that says "(Search mode)..."
- Select a title from the new list
- Press the 'Up' or 'Down' buttons to see how it works
- To go back to normal press the big, horizontal button once more.
Let me know if you want this feature...