HKS doesn't make a dual piping exhaust. but I've had the N1 single, and I currently have the Hiper (hi-power) exhaust...it's basically the same design as the N1 single, except it's 2-piece instead of one long-a$$ piping like the N1. Sound is somewhat similar...quieter though.
if you want to stay NA and like the N1 single look...the Hiper is a good way to go.
as far as the dual vs N1/Hiper...I've heard the dual is a little louder, but supposedly it's better...don't know...also, people have had problems with the dual pipes hitting an aftermarket sway bar.
*edit* sorry, I was typing while you posted LOL
anyways...I'm not sure if that's a HKS exhaust with the dual piping...see if you can find that exhaust
here..