slider fade between a series of sound sources

Hi guys
I'm trying to work out the best way to use 1 slider to fade between a series of sound sources.

piano->harp->glockenspiel->violin etc

Here is a patch with where I'm at but the problem is I don't want the fades to be linear as the volume drops when between 2 instruments. I looked through the tutorials and found how to do this for 2 and 4 channels but I will have more than 4 instruments. I'm thinking maybe adding an exponent to the scale objects?

Many thanks for any advice.