my AAZ has 2.5" from turbo back, with a res and straight through back box.
overall noise is QUIETER than stock - but sounds nicer. a little note to it.
the k14 turbine outlet (or t2 if you have it) is so small that you get bugger all exhaust noise.
with the electronic wastegate actuation, i notice a little increase in note and deeper, throatier growl when the wastegate opens - thats how small the turbo is.
if you're going to a bigger turbo, you might wanna keep a box - but if you just have stock turbo, straight pipes is very quiet.
even with just the downpipe, my AAZ still quieter than my mk1 LS gasser.