Pixhawk2 gps module

Hi, everybody! Can’t understand how connect my m8n gps+compass module to pixhawk2. Could somebody help and explain what way is correct?
Connect GPS’s rx tx to “GPS1” 8pins connector
and Compass’s SCL SDA to “I2C2” 4pins connector
or connect everything to “GPS1” 8pins connector and do not use “I2C2” 4pins

Question appeared after I read included in package “pixhawk 2.1 user manual” and downloaded “pixhawk-2-17th-march-2016 feature overview”

If you have the old GPSs connector, there is a cable that has the 8 Pin connector in one side, and the 12c female with a female where you can connect with the previous Pixhawk one connectors. I you have the Here GPS it should be connected directly. Do you have any pictures of your GPS cables?

Have old one for apm 2.8

gps cable

In manual very simple scheme and it is not explained. Why need connect compass to I2C2 (scl sda) when GPS’s connector already have same pins, but there is difference in direction of pins. And there are two different I2C bus what is for what?

[details=pixhawk connector spec]