Hmmm, there is a lot to consider about what you actually want besides the stereo. There is a whole industry to upgrading your tunes in any vehicle if you choose.
If you only think about the variants of the Coupe and the GS, the notable differences in the vehicles start with both being a Grand Touring car, but the coupe has more creature comfort/amenities in the cabin. The GS is a simplified, no frills interior which might be more suited to very occasional driving or shorter trips.
Outside the cabin there are several additions to the GS that might not be on the coupe: installed x pipe and the active sport mufflers (not sure if this was a coupe spec also). This basically just equals a louder exhaust and minor performance. Lots of other details that I'm not covering since you can find lots of side-by-side comparisons online, but you have to ask yourself what you are wanting in a weekend car.