  We present a 6D orbifold model on $T^2/\Z2$ which emerges as intermediate
step in the compactification of the heterotic string to the supersymmetric
standard model in four dimensions. It has $\SU6$ gauge symmetry in the bulk and
two pairs of inequivalent fixed points with unbroken $\SU5$ and $\SU2 \times
\SU4$ symmetry, respectively. All anomalies are cancelled by the Green-Schwarz
mechanism. Two quark-lepton generations are located at the $\SU5$ branes, the
third family is composed of split bulk hypermultiplets. The model has vacua
with partial or full gauge-Higgs unification and non-vanishing Yukawa couplings
which generically avoid the unsuccessful $\SU5$ mass relations.
