EDIT: ... or it could be 'A' for Audition.

However, there seem to be quite a few parameters that don't add sound, but rather modify the basic preexisting sound (such as the impedance of the soundboard). How would one "solo" a parameter that does not itself produce a sound? Or perhaps it is not important to be able to isolate those parameters for testing or experimentation purposes.

So I'm deep into programming a Pro sound, and even though I'm reasonably familiar with the parameters now, I still find myself yearning for a 'Solo' button beneath each Spectrum slider, the Duplex Scale/Aliquot strings, Sympathetic Resonance, the Action sounds - basically any parameter that adds its own sound.  The idea is that you would hear the contribution these sound-producing parameters make in isolation, so you could better understand exactly what they contribute to the overall sound.

As I'm sure many of you have found with Pro, so many parameters make important but sometimes similar contributions to the sound, it can be hard to be 100% sure how they all interact when you tweak.  Sure, you can temporarily set a parameter really high (eg. push a spectrum slider all the way up or down) to more clearly hear what it does.  But I think a way to solo-audition them would be even better - a) it's faster and b) you would hear what the parameter does at its current setting, which makes it easier to understand exactly what it contributes as you toggle Solo on/off.

I'm thinking a little clickable 'S' icon next to each relevant parameter - it could be small so it doesn't get in the way

Would anybody else find this useful?  Vote!