the ti trs yoshi is the best exhaust for the drz, but it is hard to find because yosh quit making them, The RS2 and RS3 are also really good, but whatever you get you need the full system dont waste your money on a slip on there is no benefit other then noise.
I have an "08" DRZ with a White Brothers E2. Do the 3X3 mod., and a dynojet stage 2 kit. Run the clip on #2 position with a 155 main. Change the pilot jet to a #27.5, and back the air screw out about 3 1/4 turns. If you don't do the pilot jet, you will get lots of backfires on deceration
Agree with t.dot the ti trs yosh is the best. You might be able to source one from Japan but it will be $$$. The ti TRS yosh sets up your bike to have more mods done to it. The exhaust works so well you will need NOT to change to another exhaust if you do internal mods (cams, bore, stroke, and etc.).