And If I understand correctly, my German permenet residence card's maximum validity is the same as my passport.
Note: the card will become invalid, your permanent residence status continues.
Should I inform the Auslanderbehörde beforehand?
You should definitely inform the responsible Ausländerbehörde before the passport expires.
That is because males can't renew their passports, from my embassy, until the final exemption from the military service which will be after two years for me.
Such situations are generally known by the Ausländerbehörde, so they will probably not be surprised.
You should make an appointment at least 6 months before the passport expires, informing them of the situation.
The result will probably be that they will issue a foreigners passport (travel document), if the conditions to obtain your national passport will be considered unreasonable.
Travel document - Reissue
Acquisition of a (national) passport must be unreasonable
A passport or substitute passport from the country of origin cannot provably be obtained in a reasonable manner. A reasonable manner constitutes in particular the timely application to the relevant authorities of the country of origin for the issuance or extension of the passport, and the payment of the fees stipulated for this.
§ 5(2) AufenthV lists reasons that are considered as reasonable efforts that the applicant must attempt:
(3) military service, unless its fulfillment is unreasonable for compelling reasons, and to fulfill other reasonable civic obligations.
So the avoiding of military service alone may not serve as a valid reason to be issued a Travel documents for foreigners.
So a person who has actually been called up to serve their military service may be treated differently than someone who may be be called up to a specific age (in Germany this was up to the age of 28/32 (§ 5(1)(2,3) WPflG) ).
For the latter case it is known that a Travel documents for foreigners has been issued, since to refuse the issuing of a passport for someone who might be called up was considered unreasonable.