  We reveal in this study the fundamental low-energy landscape in the
ferrimagnetic Sr2CrReO6 double perovskite and describe the underlying
mechanisms responsible for the three low-energy excitations below 1.4 eV. Based
on resonant inelastic x-ray scattering and magnetic dynamics calculations, and
experiments collected from both Sr2CrReO6 powders and epitaxially strained thin
films, we reveal a strong competition between spin-orbit coupling, Hund's
coupling, and the strain-induced tetragonal crystal field. We also demonstrate
that a spin-flip process is at the origin of the lowest excitation at 200 meV,
and we bring insights into the predicted presence of orbital ordering in this
material. We study the nature of the magnons through a combination of ab initio
and spin-wave theory calculations, and show that two nondegenerate magnon bands
exist and are dominated either by rhenium or chromium spins. The rhenium band
is found to be flat at about 200 meV ($\pm$25 meV) through X-L-W-U
high-symmetry points and is dispersive toward $\Gamma$
