I had to have the centre box cut out of mine due to it splitting it's welds after playing with an Audi S3 and while it wasn't too bad on idle (still proper loud though!), on the motorway and on boost it was way too loud for my liking! The noisy exhaust and the whine of the straight cut gearbox made it horrible on long trips!!
I would keep the centre box if I were you. Personal choice obviously!