Try working with the adjusters. I'm almost the exact same size as you (6'0", 185 lb) and my initial impression was that I HATED the seats. Turns out the problem was how I had the seat cushions adjusted.
My previous car had a very low roof (Toyota Celica) and the rear of the seat cushion was adjustable. I had to run it all the way down and with the seat somewhat reclined to fit in without my head touching the roof. When I got in the 370Z, the first thing I did was crank the rear of the seat cushion all the way down and the front all the way up. The 40 mile drive home from the dealer was in a word miserable. I felt like I was sitting in a hole and my back felt like the support was in all the wrong spots. By the time I got home, I had a serious neckache.
What I later realized is that there is much more headroom in the Z and the shoulder bolsters are much more pronounced than in my Celica. What you need to do is crank down the front seat cushion and then adjust the rear until you feel the shoulder bolsters hitting you in the right spot. Then adjust the front cushion until the seat feels good.
The stock adjustments basically give you the ability to make the seat horribly uncomfortable. I've since taken trips of around two and a half hours in the car and felt great the whole time.
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