  One of the challenging tasks at future experiments is the clear
identification of the underlying new physics model. In this study we
concentrate on the distinction between different supersymmetric models, the
MSSM and the NMSSM, exploring the gaugino/higgsino sector as an alternative to
the Higgs sector. Under the assumption that only the light chargino and
neutralino masses and polarized cross sections $e^+e^-\to
\tilde{\chi}^0_i\tilde{\chi}^0_j$, $\tilde{\chi}^+_i\tilde{\chi}^-_j$ have been
measured, we perform a fit of the fundamental MSSM parameters $M_1$, $M_2$,
$\mu$ and $\tan\beta$ and study whether a model distinction is possible. We
focus here on the challenging cases of scenarios with a relatively heavy
singlino and address two classes of neutralino mixing,
$\tilde{\chi}^0_1\sim$higgsino-like versus $\tilde{\chi}^0_1\sim$gaugino-like.
