u cant, that's wack as hell. the jjos 5.01 is missing the continuous sample playback function in the other screen. i gotta have that to single out my sample tracks. it sucks having to wait 4, or 8 bars just to have the sample mute.
in track mute mode press "window" button to set the mute of one shot sample to immediate.
or record the sample in "note on" mode to have it stop immediately.