If you want the loudest bike possible, get an MJS header and your choice of slash cut slipon (Graves, Jardine, Akrapovic, Hotbodies, Racefit slashcut). Trust me, you don't want your bike that loud. I took the canister off of my M4 full system and started it up. Sounds like shit IMO and you'll probably lose some hearing riding around like that. If you want a decent sound that is still loud as **** get a Racefit Growler.
Akro carbon, it's pretty loud(deep and smooth) also has sound dampening insert that you can install if you ever wanted to quiten it up a bit. I think the new hex design of there can looks great with the lines of the bike. I had both leo and the akro laying side by side in my garage and I thought the akra was the better choice workmanship quality and looks.
I got a Termignoni GP on my 08 R6. I have owned a heap of bikes over the years and had most major brands of exhausts. Last Blade had a full Akra Evo Titanium System. The Termignoni GP was specifically designed for the R6 for Supersport, it's the real deal. The quality is excellent and the sound is amazing. If you want loud, remove the cat and add a Y-pipe. Next best choice is an Akrapovic. As far as i'm concerned, everything else is junk.
Termignoni = Italy
Akrapovic = Slovenia
Most other manufacturers say their pipes are 'handcrafted' which means they make that shit in China!
I'll post a vid up soon, let the pipe do the convincing!