Been 4 years since I posted this thread and still don't know which exact method Spoon used!
However having learned alot since then, its not hard to figure out they just simply would off used a cold air feed ducting pipe, attached to the bottom of the airbox, going straight behind the arch liner area. Instead of having a silly ducting pipe sticking out the front bumper. An engine can only take in so much amount of air.
Having tried various airboxes myself with bseries and kseries, its quite evident that enclosed air boxes like Mugen or groupe m etc work better for the obvious reason as you all probably know.
Look at the mugen intake, its the same design as the dc2 intake but much bigger in terms of filter and piping.
If your on a budget I would stick to the oem dc2 airbox and intake pipe (ek owners will have add and additional hold for the air temp sensor very easy job and also an airbox bracket) attach a cold air feed ducting pipe directly into the bottom of the airbox going straight behind the arch liner or where the standard resonator sits. Works well on mine.
You can actually use the standard dc2 resonator as a cold air feed ;-) this way you dont need to mess about with the duct pipe. Will post a pic of how I modified the resonator ..