First, you must draw out in pencil the limitations of the vinyl opening based on the diameter of the speaker basket. The center of that hole must be perfectly aligned with the concealed structural hole behind the vinyl. Then you have to decide how you will terminate the vinyl so that is does not wrinkle or stretch over time and with temperature extremes. You don't want the vinyl terminated by just the speaker mounting holes or clamped down by the speaker frame only. You can either cut out a circle or cut a pie pattern depending on how you plan to terminate the vinyl. You can first cut a starter slit with a razor blade and then use quality scissors. Cut the vinyl first and cut the foam padding separately.
Odin with Earmark provides his customers with a detailed step by step procedure that includes several illustrations. The procedure also addresses a variety of techniques for terminating the vinyl, managing the speaker depth in thick foam, and cutting out the back of the polymer bolster plus cutting the fiberglass mold when an existing hole is not provided from factory.

David