  We describe a setup for performing inelastic X-ray scattering measurements at
the Matter in Extreme Conditions (MEC) endstation of the Linac Coherent Light
Source (LCLS). This technique is capable of performing high-, meV-resolution
measurements of dynamic ion features in both crystalline and non-crystalline
materials. A four-bounce silicon (533) monochromator was used in conjunction
with three silicon (533) diced crystal analyzers to provide an energy
resolution of ~50 meV over a range of ~500 meV in single shot measurements. In
addition to the instrument resolution function, we demonstrate the measurement
of longitudinal acoustic phonon modes in polycrystalline diamond. Furthermore,
this setup may be combined with the high intensity laser drivers available at
MEC to create warm dense matter, and subsequently measure ion acoustic modes.
