When panels are in series, the voltage adds but the current stays the same. When panels are parallel, the voltage stays the same and the currents adds, so this is the basics that you are missing
The minimum operational voltage for the Xantrex GT3.0 is 195V and I would recommend nothing less than 220-230 vmp typical, or about 14 of the 80 watt panels 12volt nominal panels
Xantrex has a nice string sizing tool on their web-site, located at:
http://www.xantrex.com/support/gtsizing ... p?lang=eng
I used the above tool and it agrees with my guess, 14 12volt nominal panels would be the smallest array you could have, the current is only about 4.6 amps so I would use 10 gauge which is about 70 bucks for 500ft at home depot.