I'm new to all this so ... i don't understand what your on about, this is my first car, sorry for being such a succkaa (Y)
ok from the engine youve got the
exhaust manifold - 4 pipes from the engine
downpipe(s) - on a turbo this is directly after the turbo, none turbos its part of the manifold
cat- catalitic converter
centre section - from the cat to the back box
back box - the rear most silencer, the thing youve posted up.
to gain performance you want the gases to get out as fast as you can (this doesnt mean put on the fattest pipe you can find as the lower pressure means the gases come out slower, too small a pipe and it will choke up the engine)
as HDI has said all the bends will slow down the gases, you could be making more noise but have less power
as for exhausts you can get off the shelf ones deisinged for the car, or custom built ones from the likes of powerflow.
or then you get univerial which fit 0% of cars