The only thing the EXR-7 has over the 3K is probably 76 key and the overall quality of those keys (and having a joystick for pitch/mod). The PSR-3000 (internally) is far superior to the EXR-7. The EXR-7's keyboard would make a nice controller for the PSR-3000 though.
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.