You can get to the DV with trolley jack and axle stands it's under the car, drivers side.
A diverter valve isn't the same as a blow off valve. Wouldn't recommend a BOV as it can be bad for boost, if you haven't got a problem at the moment then stay as you are.
Best thing to do is get rid of the standard air box and replace with an open cone filter/induction kit.
Brands like ramair or revo do them. If you're considering tuning your car then the sound will get even louder because of the higher turbo pressure in the map.
It depends on if you're getting a custom map (that takes into account your mods) or a map from revo/apr etc. You would be best to have the car setup before going into the map.
But if I'm honest an induction kit is mainly for the noise, but does let a bit more air in that might slightly benefit the turbo.
From my induction kit it certainly sounds like you have darth vader under the bonnet and with every gear change get a tssssh.
Let us know how you get on
Let us know how you get on