My new boat comes with an ST 6001 Autopilot. I would like to get the
benefits of the AST feature and the gyro stabilized compass improving
my MARPA results

As close as I figure, there are two ways to do this.
a) Add the gyro stabalized compass to my existing ST 6001.
b) Replace my core-pack with an SG1 corepack.

My questions.
1) What is the difference, if any beween doing either of the above ?
2) Can I trade in my unused S1 corepack for an S1G core pack ?