MAD is not the AF hub.

You can only have a stopover at CDG when flying on this ticket (Your journey is Boston to Hong Kong; you are travelling on AF so that means you are routed through Paris; Madrid is not en-route so you cannot "stop off" there).

A stopover is when you take a longer break than you actually need to on a ticket that, by necessity, cannot be flown directly but requires you to stop somewhere to change planes to continue to your "real" destination. You can only have a "stopover" at such a place, where it is necessary for you to change planes. You cannot "invent" an illogical stopover point at a place of your own choosing, such as this unnecessary side-trip to Madrid

But why would you even want to book it this way? Book it as two separate tickets (ticket 1: BOS-MAD: ticket 2: MAD-HKG), exactly as you have posted.