Tune required if you have a catless x-pipe, meaning the cats are removed from you x-pipe (mid-pipe same thing). You can also have high-flow cats which would require a tune and have less smell than a catless one.
No tune required if you are just changing the axle-back portion of the exhaust but then keep in mind that no power will be made and only sound.
As a couple of people have said, Eisenmann Race is the way to go. Akra would only be worth it in my opinion if you get the full evolution system (used 5 grand, new about 6.5 grand).
I'd stay away from hyped system such as the iPE etc but if you really have money to burn then nothing can beat the Kreisseg system or the Akra slip-on with GT4 x-pipe (easily 8 grand).
If you want a great sounding system that makes around 40 horses then go for one of the following; eisenmann sport + challenge race x-pipe (catless), gintani sport + gintani catless x-pipe and finally my favourite RPi GTM full system (makes most power with a tune).
Also, don't forget that resonators are your best friend unless you just want to be stupidly loud. They help define the pitch and tone of an exhaust + help to eliminate any drone. If you want NO drone then performance exhaust (alone with no catless x-pipe) or Akra EVO are your best bet.
Hope that helps!