When my 2004 was stock, I went to FMF Fattys with turbine core 2's, tors removed, K&N pods, and droped to a 13 tooth sprocket on the front. Had tons of low & mid range, and you will not get hassled for sound. Went with 20X20X10 8 paddle Haulers. It is a dune only bike ridden at sea level!
Hope this helps