Here is what I have tried. In all cases I am runing a K&N airfilter and stock M&M EFI. The stock pipes, changes the fishtails to cones, no noticable difference. Tried White "E" slip-ons very nice sound, and my mid range ran smoother and I had a little more power, it sounded really good. 8 Discs on the left pipe, 11 on the right. Then I tried a Supertrapp slip-on with 8 discs on the left and 12 on the right. I liked the White "E"s better. Seemed to have better performance and definitely sounded better. Then I tried the 2 into 1 SuperTrapp - WOW. Made a significant improvement. I was initially woried that I should be concerned about the EFI map since I figured it was running leaner so I would need to do something. I ran the scooter for about 1000 miles and was going to install the Screaming Eagle Digital Fuel Optimizer. But when I took it in I mentioned to the tech that I was getting significantly more power, my fuel mileage was about 4-6MPG better, and the oil temperature was running about 10 degrees lower (easy to determine, when riding with my wife we would compare bikes and I saw a 10 degree difference after installing the 2 into 1). The tech checked plugs and said they could not look better!! And the sound was simply beautiful!!! I really, really like the 2 into 1 Supertrapp. The only down side is, I think a touring bike should cosmetically have duals and after about 6000 miles the header pipe cracked on the rear cylinder. Supertrapp warranted the header and replaced it for shipping costs only. In the mean time I went back to the Supertrapp slip-on duals. That gave me a chance to play around with duals again and I can conclusively say that the 2 into 1 has significantly better performance and we never installed the DFO. The bike configuration runs so good with the 2 into 1 Supertrapp we decided to leave the EFI alone. So I am very happy with the K&N, no mods to the M&M EFI and the 2 into 1 Supertrapp. Runs good, sounds great, looks OK!