I like the second of your answers—]Or is it because they have no talent or taste that they do not mix much more with society other than their children (Lady Middleton) or such people as can be rounded up for amusements at the Park? :D

I read total want “of talent” to mean Sir John and Lady Middleton are untalented, have no other resources to occupy themselves other than what is described—his as a sportsman, congenial host and hers as a mother, cold but elegant hostess. I take total want “of taste” to mean neither of them desires to pursue any other resource, activity, pleasure. Their employments are confined but that is how they like them. So in the end “total want of talent and taste” means they have little resources with which to occupy themselves but they are happily satisfied with what they have.

In Chapter 7 it is noted that Lady Middleton gave up music immediately upon her marriage—when she no longer needed to attract a husband. Music to her was a throw away resource, useless because neither she nor her husband enjoy it—neither her in making it nor he in listening to it. Evidence for this is when Marianne plays the pianoforte in Chapter 7, neither Sir John nor Lady Middleton pay attention but continue in their chosen pursuits. Sir John continues very loudly in his role as congenital host and Lady Middleton tries to maintain an elegant listening personal as a good hostess but is not paying attention at all because she asks Marianne to play a song she has already played.

I think “unconnected with such as society produced, within a very narrow compass” means Sir John and LM are not influenced to improve themselves by the few talented resourceful individuals found within their small society and I think their behavior during Marianne’s requested recital is proof of that.