There are some cool tricks you can do with the Roland BK9's...

You not only get a dedicated 'Track Mute' button, which can be programmed per Performance which track or tracks it mutes, but the D-Beam can also be tasked to switch off drums, drums and Bass, or everything BUT the drums and bass.

So, by a combination of these, you can have considerable flexibility choosing what you want to quickly mute with one button or a wave of the hand. The thing about all this, at least for me, is that I don't want to have to go and grab sliders or hit a bunch of buttons to do ONE thing, and I don't want to have to repeat the whole process to turn everything back on...

But damn! Sure would be cool to have the machine figure out 'Hey, he selected an acoustic piano... I should mute the Piano Part! Oh... now he's got a jazz guitar sound. Let's turn the piano back on and mute the guitar part now.'

THAT'S a smart arranger!