Hey Ive just looked into the product your on about, what kind of keyboard do you have?.. is it a midi controller or a synth?.. aslong as it has a 1/4" output you can record into the tascam device.
As far as the "duplicating" goes.. Im not sure but you can double track the part you want to record onto a separate track which would duplicate it.
Hope this helps... Dont know much about the products your using so i couldn't state much detail.