Honestly, sticking with MR2 turbo cat-backs makes more sense. They bolt right up to the stock brackets and flow enough for your average V6.
You have more to gain from modifying the actual exhaust (and not some overpriced shiny muffler), anyway
Stock VZ/MZ manifolds suck!
As for sound, you're not going to get a 6-cyl to sound like a 4-banger. Sound has more to do with the engine (# of exhaust pulses) than it does the muffler. Header'd 1MZs and 3VZs seem to sound a lot like 3.5L Nissan V6s and NSXs. That is, to say, the only other cars on the road that commonly have V6s with opened up exhausts