Questions about using menu background music in Emulation Station

[Grasshopper]

I'm using a Retropie build based around Emulation Station that provides background music when you're using the menu.

However, I've come across a couple of problems:

• I want the background music to be different depending upon which theme I'm using. So, for example, if I'm using the NES theme I want the NES background music to play, and if I'm using the SNES theme I want the SNES music to play. Does anyone know whether this is possible?
• The build is set up to use video snaps. However, when a video starts playing, the background music doesn't stop. So you end up with the menu's background music and the video's sound effects playing simultaneously, which sounds awful. Does anyone know how to stop the menu's background music from playing whilst a video is playing?

Thanks for your help.