  The potentiality of interpreting the D-meson decay-dynamics has revealed
itself to be strongly dependent on our understanding of the light-meson sector.
The statistics collected by FOCUS is already at a level that manifests
parametrization problems for scalar particles. In this paper the first
application of the K-matrix approach in the charm sector is illustrated and
preliminary results on the D+ and Ds decays to three pions are shown.
