The following THEATER 500 series speakers come with fabric speaker covers that hold to the speaker magnetically:
Floorstanding T 500 F 16,
Center T 500 C 16,
Dipole T 500 DL/DR 16
Bookshelf T 500S FR 16
Please hold the cover in alignment with the speakers and turn them carefully until the cover sticks to the internal magnets.
For example on a THEATER 500S: