  We consider a quantum dot with ${\cal K}{\geq} 2$ orbital levels occupied by
two electrons connected to two electric terminals. The generic model is given
by a multi-level Anderson Hamiltonian. The weak-coupling theory at the
particle-hole symmetric point is governed by a two-channel $S{=}1$ Kondo model
characterized by intrinsic channels asymmetry. Based on a conformal field
theory approach we derived an effective Hamiltonian at a strong-coupling fixed
point. The Hamiltonian capturing the low-energy physics of a two-stage Kondo
screening represents the quantum impurity by a two-color local Fermi-liquid.
Using non-equilibrium (Keldysh) perturbation theory around the strong-coupling
fixed point we analyze the transport properties of the model at finite
temperature, Zeeman magnetic field and source-drain voltage applied across the
quantum dot. We compute the Fermi-liquid transport constants and discuss
different universality classes associated with emergent symmetries.
