Well its very hard to make the boxer engine sound like a ricer Honda so you don't have to worry about that. I recommend some sort of engine management to get your throttle response a little better and pretty much any turboback exhaust will get you the throaty sound. How loud do you want it? If you want LOUD you could go w/ any type of downpipe and piece it with a HKS hyper-ti or carbon-ti catback (not sure what it is called) or TXS RFL-Ti muffler/catback. Some of the quieter catbacks are the Borla Hush and Greddy EVO and EVOII I think. As for downpipes you could get anything thats mandrel bent, is divorced wastegate or bellmouth, and is 3" or bigger. Helix, TurboXS, Stromung, and Invidia are all examples, but there are many more out there.