The on board sounds (and the EXP board sounds as well) will give you all the tools you need to "customize" the sound you are looking for. The attack portion of the piano sample can be taken out, accordians can be layered and detuned - you have to get into the editing section now. No one manufacturer can predict what every listener will like, so you have the power to change the sounds, and alter them to your liking.
Try messing with the accordians - use two different samples (tones) and detune one slightly - this will get you closer to the sound you described. Also try a little chorus or flanger (light) to add that "motion" sound.
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