An exhaust system is basically a pipe (aka downpipe) connected to the outlet (exhaust valve) side of the cylinder head.
Usually, there is a muffler, a box of continuous piping going backwards and forwards. The piping in the muffler is full of holes and the muffler box is stuffed full of non-flammable sound-insulating material. The muffler is designed to prevent sparks from leaving the exhaust system and make the exhaust quieter.
Usually, the downpipes in a multicylinder bike are joined. The length of the pipe before the join has an influence on sound and power. The exhaust might also branch out after the muffler. So, a 4 cylinder bike with The pipes joining together and dual exhaust outlets is a 4 into 1 into 2. Joining pipes together helps 'scavenge' exhaust gasses. The join acts as a venturi, saving engine horsepower to push the gas out. When this approach is used the length to the join is important, as it changes, it changes where the exhaust is most efficient and contributes to horsepower gains.
Where things get complicated is modern vehicles, including motorcycles, have catalytic convertors (cats) to help turn toxic emissions into less toxic substances. A catalyst is a form of chemical reaction. Catalytic converters are usually large, heavy, and ugly. Some bikes, including the supersport, combine the muffler and catalytic convertor. On the supersport it's hanging under the motor. The two outlet pipes (cans or as you call sleeves) have some form of muffling characteristics, but there are minimal at best. That's why there is little difference in changing the outlets for aftermarket items. They are similar to the straight-through mufflers we used to call hotdogs when we were modifying cars, but they need to be as long as possible to bring the noise down to an acceptable level. It must be said, however, this style of muffler produces a deeper sound. They are sometimes called a resonator if they are used after a muffler in an exhaust system.
If you want to make a real difference to sound, the muffler/ catalytic convertor has to go, it's where most of the noise is lost. You are then left with a straight-through system that is loud. Straight through mufflers can be added to the system, but due to the fact they are short they are not overly effective at reducing noise.
That's where a baffle comes in. It is designed to quieten the exhaust. A crude form of baffle would be to pack the muffler with steel wool, but it results in a loss of power due to being overly restrictive and would soon oxidise.
In general, the speed of the exhaust gases contributes to the noise the system makes. Exhaust systems try to slow the gas flow down by letting it expand into larger areas or by disrupting the flow.
The cheapest way to make the supersport sound better is to remove the servo that operates a mechanical baffle (valve) in the exhaust system and leave the baffle in the open position. You need an 'exhaust healer', an electronic device costing about 80 bucks to fool the ECU into thinking the exhaust valve is working. If not, you get a check engine warning light. This mechanical baffle or valve reroutes exhausts through more muffling under certain circumstances and is used to help pass emission's standards including noise. If you accelerate gently you should hear it opening at about 3,000 RPM (might be different for the Euro 5 compliant 950) and the exhaust note changing.
The next cheapest way is to remove the catalytic convertor and 2 exhaust outlets and replace them with another muffler. This is the approach used by Competition Werks and Delkivic. You can run this style with or without baffles, but anecdotal evidence suggests the baffles are a must. A local bike exhaust specialist might be able to make a custom system along these lines for you. Sometimes these are just advertised as a muffler and the installer needs to make pipes to replace the catalytic convertor and connect the muffler to the downpipes.
The last, and most expensive, approach is the full Akrapovic system. This system has been designed for the bike and will have the greatest performance benefits. Again, the choice of baffles or no baffles.
If you go down the paths that remove the catalytic convertor it is more than likely it will upset the engine management system (in the old days we had to reject the carbies to get the bike to run smooth and get performance gains). This is where an upmap comes in. It changes the ECU so it matches the exhaust.
One thing to consider is a loud exhaust can be fatiguing on long runs at constant revs. A loud exhaust and induction roar is alright playing in the twisties but not as nice commuting or touring.
Hope this helps.
