Sorry not been on forum for a couple of months... so to an extent this is in case others are searching... as the OP may have already found the answer.
In the i30, at least the FD body (of which 2009 is), the steering audio controls (to the best of my knowledge) are simply switches that connect a resistor (each switch has a different value resistor) between two wires.
I can't seem to find any technical info (such as what the function of each coloured wire) on the SWC-C20 - so can't really provide much advice as how to wire.
However, unless the SWC-C20 can be custom configured (e.g. put into a learning mode or some such), it still might not work as desired - as it will probably have a default mode suitable to one or another make/model of car. Also it would depend on if the SWC-C20 is actually designed for resistance based control or is actually a CAN-BUS reader/converter (to translate CAN messages from the controls to the head-unit)