Addition of rigid poly(styrene-co-maleic anhydride) (SMA) to a polyamide-6 (PA-6) matrix leads to a system with increased stiffness and unchanged toughness as a consequence of absorption of deformational energy by the plastic deformation of brittle inclusions together with the matrix. The range of properties of both components, where this effect occurs, was studied. In addition to the use of various PA-6 and SMA types, PA-6 was also modified with epoxy resin, as well as SMA with liquid rubber bearing amino groups. Owing to the crosslinking ability of both modifiers, the influence of the changed deformability of blend components was demonstrated. Simultaneous influencing of rheological properties and reduction of the amount of reactive groups usable for the in situ compatibilizer formation make it possible to vary the size of dispersed SMA particles and the interfacial adhesion. Thus, a more comprehensive insight into the behavior of ductile-brittle blends is gained. As SMA and modifiers have negative effect on the PA-6 crystallinity, comparison of the obtained data with model calculations is difficult.