I would say that the usage "the full buffet of satisfaction" implies that there is only one "buffet" to be considered, that the author knows what it is, and expects the reader to agree. This usage is grammatical, and natural, but it subtly invites the reader to take an unstated opinion for granted. Hand the author written "a full buffet of satisfaction" thyat would have iplied that there are several, perhaps many, ways for a marriage to be fully satisfying.
In short, this use of "the" is correct, but it changes the meaning from what it would have been if "a" had been used instead.