The sampler sound cannot be monitored with the headphones.

When the [HEADPHONES MIX] control of the unit is turned fully counterclockwise (when only CUE of the channel is selected), press the [SAMPLER CUE] button to select [SAMPLER CUE].

When the [HEADPHONES MIX] control of the unit is turned fully clockwise (when only the MASTER CUE is selected), slide the [SAMPLER VOLUME] fader away from you.