Very cool app and a nice evolution since the first beta!
The list is not in the cycle chain, and so can't be controlled via keyboard.
Could you add right-mouse-click over a sample in the Soundboard to stop a sample?
If no images for a music/sample is defined, maybe write the name into the brush (in the Soundboard) at the bottom?

At the first press on the Soundboard icon I wonder what happened, because I didn't had the second monitor switched on;)