it sounds more NA as its connnected up to a bigger V8. to kill the turbo noise in the exhaust, i suspect your looking at smaller exits, possibly several, like 2 sets of twin exits. (jag Style) smaller diameter pipe. maybe some resonance chambers. like on the motordyne exhaust HFC's. but all that will affect performance, you'd sacrifice performance for noise. and even then i don;t think it will help i think it will just be quieter.
i think you have to quieten the engine down. less intrusive waste gates etc.
or maybe look at adding an electronic exhaustvalve fitted near the manifold side of the exhaust, that gives the better noise.
to be honest the zed engine even with a decent exhaust never sounded as good as i'd hoped, and thats cos its missing 2 cylinders, the zed was a m ore racey noise if that makes sense, a bit raspy higher reving etc. tuned to run smooth and not with a lumpy idle.