Jitter Geometry Question

Hi All,

I have a rotating 3D cube and am trying to use it to fade between 6 different audio samples. I have worked out a way of doing this on the x axis using if objects but am struggling to find a way to work out the y axis also.

The general idea is that each face has a sound assigned to it and by spinning it three dimensionally you can fade between each of these sounds. When a face is flat to the camera it is at full volume and fades out as less of the face is visible.

Im guessing that there is some geometry maths involved but I have no idea on what this equation may be or how I could implement it.

Any help would be greatly appreciated

Many Thanks

Jamie