In older Ubuntu versions I could right-click on a folder and I would have the option to open it with Audacious. I can't in 13.04.
P.S.: I don't know what thunar is.
This is the way I did.
I ran the following command:
Then run the Nautilus-Actions Configuration Tool, and create a new item:
If you set the 'view', 'interface' to winamp, and then 'view', 'always on top' audacious is small and always displays. Then its really easy to drag and drop folders into it. Just something I tried, and it worked...