You can often buy digital-only access directly from NT2.nl without repurchasing the physical book.
The audio fragments in De Opmaat are not just "extras"—they are integral to the 10 thematic chapters that cover everyday situations like making appointments, health, and work. De Opmaat Audio Free
Some introductory modules or sample chapters are occasionally available for free on the publisher's site or through language schools like ABC Dutch to give you a feel for the material. You can often buy digital-only access directly from NT2