  We report on the first integration of novel magnetic microcalorimeter
detectors (MMCs), developed within SPARC (Stored Particles Atomic Physics
Research Collaboration), into the experimental environment of storage rings at
GSI, Darmstadt, namely at the electron cooler of CRYRING@ESR. Two of these
detector systems were positioned at the 0$^\circ$ and 180$^\circ$ view ports of
the cooler section to obtain high-resolution x-ray spectra originating from a
stored beam of hydrogen-like uranium interacting with the cooler electrons.
While previous test measurements with microcalorimeters at the accelerator
facility of GSI were conducted in the mode of well-established stand-alone
operation, for the present experiment we implemented several notable
modifications to exploit the full potential of this type of detector for
precision x-ray spectroscopy of stored heavy ions. Among these are a new
readout system compatible with the multi branch system data acquisition
platform of GSI, the synchronization of a quasi-continuous energy calibration
with the operation cycle of the accelerator facility, as well as the first
exploitation of the maXs detectors' time resolution to apply coincidence
conditions for the detection of photons and charge-changed ions.
