What you are talking about is called "mix-down". It’s indeed an issue here. But I don’t believe that reducing volume of my part during playing is solution here. You know that if a singer doesn’t hear his voice in monitors loud enough his singing will seem like struggle. PSR keyboards aren’t able to route parts to different outputs, that’s why we can’t do everything right during life performance. Well, I’m just trying to let it go for now.

As for the expression pedal, I have such thing from M-Audio and it works well. I tried FC-7 and it didn’t seem to me to be much better. Actually, the one from M-Audio let’s you to change its straight by turning a small wheel on it. You can make it to change the volume only slightly, not the whole way.