Now that we're finally getting somewhere with this topic, Id like to offer my advice because like you I research heavily into modifications. I built my B18 engine myself, fully self taught.
The one overwhelming part that I've noticed with exhausts for 350zs is rasp, and this is where you really get what you pay for out of the box. I'll be honest ive been gobsmacked at how much a V6 can rasp. While various options like true duel, single exit and the like massively depend on the person at hand, if you want to avoid rasp you're going to have to put money into it.
Before I fitted my HFCs, I had a japspeed K2 Y pipe, centre pipe and backbox. Rasp was minimal, with a deep throaty burble on idle. Continuing through the range it remained consistent and even at WOT it wasnt droney. Upon fitting of japspeed HFCs, its changed the exhaust note massively. Town driving it sounds lovely, that real V6 worrble thats borderline skyline sound (imo just with boost) and I love it.
However, due to the increased flow and heat, at anything over 4K or WOT its become raspy as hell, Honda levels of rasp. An added issue ive encountered is possibly a design fault in mine, that the baffles rattle from resonance which we all know is horrible. Ive put this down to the fact that after HFCs, there are no baffles slowing it all down before it hits the backbox. From looking online and if money was on trees, Id purchase an Invidia gemini with ARK HFCs. These have a resonance chamber built on the side and although I appreciate that most recording devices aren't going to pick it up perfectly, near 0 rasp.