  We consider a 6-dimensional supersymmetric SU(6) gauge theory and compactify
two extra-dimensions on a multiply-connected manifold with non-trivial
topology. The SU(6) is broken down to the Standard Model gauge groups in two
steps by an orbifold projection (or Wilson line), followed by a Wilson line.
The Higgs doublets of the low energy electroweak theory come from a chiral
adjoint of SU(6). We thus have gauge-Higgs unification. The three families of
the Standard Model can either be located in the 6D bulk or at 4D N=1
supersymmetric fixed points.
  We calculate the Kaluza-Klein spectrum of states arising as a result of the
orbifolding. We also calculate the threshold corrections to the coupling
constants due to this tower of states at the lowest compactification scale. We
study the regions of parameter space of this model where the threshold
corrections are consistent with low energy physics. We find that the couplings
receive only logarithmic corrections at all scales. This feature can be
attributed to the large N=2 6D SUSY of the underlying model.
