I would like to know what the maximum rating of the speaker impedance is. So
that the ad557 can provide the current.
The maximum output it can sink is 5mA.
The same is true for the (very similar) AD558.
This means that only transducers with high impedances can be driven directly
with the AD557 (1000 ohms or more).
You can add a current booster as shown on the AD558 datasheet, page 6 , Figure
Neither AD557 or AD558 look like good choices for audio / AC outputs.
The AD5330 would be a better more modern choice.
Another IC , AD7801 , has a higher output impedance but at least both these
are rail to rail output modern devices.
The AD557 and AD558 were introduced in the early 1980's.