Since your GTV is 3.0V6, I would recommend to try " MEXC-S (front pipe and rear)" with metal catalyzer.
As I introduced you the sound above, it is really great.(Price is also great
Pronounce MEXC-S as "mex" or "mecks".
It stands for Miyamoto(craftman's family name) EXhaust CraftS.
The products are available for GTV,155,156,147,166,and ES30. Actually not only for Alfa, but also for the other cars.
If you want to get "High tone sound" like Ferrari and "high quality" (using SUS304 by TIG welding),MEXC-S is the best buy. Over is the second place.
I think it depends on the user's feeling anyway.
I have ever heard the sound of SS, Novitec, REMUS,ANSA and so on. From my point of view, the European Exhausts sound powerful and rough.(it depends on the system, but generally speaking so)
I don't want to express my impression about European Exhaust systems so much in thie European web site wink But you will absolutely be satisfied with Japanese exhaust systems if you get one.
I think also European muffler(stainless steel made)+ MEXC-S(or OVER) front pipes could be enough.
I want to tell you that you will get some benefits from changing the front pipes.That's for sure.(sound, power and torque at middle-low rpm.)
btw, next generation of skyline GT-R will have V6 engine (Engine Type: VQ35).
Since we have voluntary restriction of bhp of stock engine up to 280bhp here in Japan, the official spec. should be also 280bhp. But potential spec. of next GT-R must be higher than current GT-R. By remapping of ECU and changing IN/EX systems, you will get over 800bhp.
voluntary restriction of Japanese auto makers doesn't make sense at all.