  Ferromagnetic spin valves offer the key building blocks to integrate giant-
and tunneling-magnetoresistance effects into spintronics devices. Starting from
a generalized Blonder-Tinkham-Klapwijk approach, we theoretically investigate
the impact of interfacial Rashba and Dresselhaus spin-orbit couplings on the
tunneling conductance, and thereby the magnetoresistance characteristics, of
ferromagnet/superconductor/ferromagnet spin-valve junctions embedding thin
superconducting spacers between the either parallel or antiparallel magnetized
ferromagnets. We focus on the unique interplay between usual electron
tunnelings-that fully determine the magnetoresistance in the normal-conducting
state-and the peculiar Andreev reflections in the superconducting state. In the
presence of interfacial spin-orbit couplings, special attention needs to be
paid to the spin-flip ("unconventional") Andreev-reflection process that is
expected to induce superconducting triplet correlations in proximitized
regions. As a transport signature of these triplet pairings, we detect
conductance double peaks around the singlet-gap energy, reflecting the
competition between the singlet and an additionally emerging triplet gap; the
latter is an effective superconducting gap that can be ascribed to the
formation of triplet Cooper pairs through interfacial spin-flip scatterings
(i.e., to the generation of an effective triplet-pairing term in the order
parameter). We thoroughly analyze the Andreev reflections' role in connection
with superconducting magnetoresistance phenomena, and eventually unravel huge
conductance and magnetoresistance magnetoanisotropies-easily exceeding their
normal-state counterparts by several orders of magnitude-as another
experimentally accessible fingerprint of unconventional Andreev reflections.
