  We investigate the equation of state (EoS) along the BCS-BEC crossover for a
quark system described by a Nambu-Jona-Lasinio model with multi-fermion
interactions. Together with attractive channels for particle-antiparticle
($\Gs$) and particle-particle ($\Gd$) interactions, a multi-fermion channel
with coupling $\lambda$ that accounts for the diquark-diquark repulsion is also
considered. The chiral and diquark condensates are found in the mean-field
approximation for different values of the coupling constants. The parameter
values where the BCS-BEC crossover can take place are found, and the EoS is
used to identify the stability region where the BEC regime has positive
pressure. We discuss how the particle density and the repulsive diquark-diquark
interaction affect the stability window in the $\Gs-\Gd$ plane and find the
profile of the pressure versus the density for various values of $\lambda$ and
$\Gd$. The effects of $\lambda$ and $\Gd$ in the BCS-BEC crossover tend to
compensate each other, allowing for a feasible region of densities where the
crossover can occur with positive pressure. These results, although mainly
qualitative, should serve as a preliminary step in the microscopic analysis
required to determine the feasibility of the BCS-BEC crossover and its
realization in more realistic models of dense QCD that can be relevant for
applications to neutron stars.
