  We extend the Fermi liquid theory of Nozi\`eres by introducing the
next-to-leading order corrections to the Fermi liquid fixed point. For a
general SU(N) Kondo impurity away from half-filling, this extension is
necessary to compute observables (resistivity, current or noise) at low energy.
Three additional contributions are identified and their coupling constants are
related using an original (and more complete) formulation of the Kondo
resonance {\it floating}. In the conformal field theory language, a single
cubic operator is proposed that produces the same three contributions with the
same coupling constants. Comparison with an exact free energy expansion further
relates the leading and next-to-leading order corrections so that a single
energy scale, the Kondo temperature, eventually governs the low energy regime.
We compare our results at large $N$ with the approach of Read and Newns and
find analytical agreement.
