I know the RS-5 is not expandable and I think there's a slot on the QS6.2 for a q-card. The RS-5 has real-time editing knobs which are sent to the MIDI out, but the QS6.2 has 4 control sliders. I think the QS6.2 has aftertouch and the RS-5 does not. I'm thinking, qs6.2. I don't know how they stand up to eachother in feel and sound though.
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Bob