Kabinopus, I don't know about any multiple touch buttons on the screen of either the 600 or the 900. Those who own one of those could give you an answer. I suspect that the capability is as it has always been on Korg touchscreens, that is, mute just the voices that are displayed. A little icon of a track's instrument is shown which, by touching it, mutes the track and an 'M' icon shows.

Yes, that's right Diki, but not forgetting that the i30 did indeed have a touch screen. Not as versatile as these newer boards, of course, but pretty comprehensive at the time. Those physical mute buttons (as is the case with physical sliders) were far more useful in live play. Korg really needs to reintroduce them on future models.