  The stability of systems containing six quarks or antiquarks is studied
within a simple string model inspired by the strong-coupling regime of quantum
chromodynamics and used previously for tetraquarks and pentaquarks. We discuss
both six-quark $(q^6)$ and three-quark--three-antiquark $ (q^3\bar q{}^3)$
states. The quarks are assumed to be distinguishable and thus not submitted to
antisymmetrization. It is found that the ground state of $(q^6)$ is stable
against dissociation into two isolated baryons. For the case of $ (q^3\bar
q{}^3)$, our results indicate the existence of a bound state very close to the
threshold. The investigations are extended to $(q^3Q^3)$ and $(Q^3\bar q^3)$
systems with two different constituent masses, and their stability is discussed
as a function of the mass ratio.
