  We present our strategy and some preliminary results for the renormalization
of four-quark operators relevant for kaon physics. We follow the
non-perturbative Rome-Southampton method, with both exceptional and
non-exceptional kinematics. We also implement momentum sources and twisted
boundary conditions. We use an (almost) unitary setup: Domain-Wall valence on
nf=2+1 Domain-Wall sea and Iwasaki gauge action, at two values of the lattice
spacing corresponding to approximately 0.086 fm and 0.114 fm . The chiral
properties of these fermions play a crucial role in this compuation and are
studied in detail in this work.
