I'm sure the PSR-2000 will allow you to turn the "voice set" off.. This is what calls up all the DSP, reverb, chorus, ect for a specific sound.. Turning this function off will get the result you're looking for.. However I'm not sure if that goes for the mixer section as well..

Squeak
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GEAR: Yamaha MOXF-6, Casio MZX-500, Roland Juno-Di, M-Audio Venom, Roland RS-70, Yamaha PSR S700, M-Audio Axiom Pro-61 (Midi Controller). SOFTWARE: Mixcraft-7, PowerTracks Pro Audio 2013, Beat Thang Virtual, Dimension Le.