  We report the discovery with $TESS$ of a third set of eclipses from V994
Herculis (TIC 424508303), previously only known as a doubly-eclipsing system.
The key implication of this discovery and our analyses is that V994 Her is the
second fully-characterized (2+2) + 2 sextuple system, in which all three
binaries eclipse. In this work, we use a combination of ground-based
observations and $TESS$ data to analyze the eclipses of binaries A and B in
order to update the parameters of the inner quadruple's orbit (with a derived
period of 1062 $\pm$ 2d). The eclipses of binary C that were detected in the
$TESS$ data were also found in older ground-based observations, as well as in
more recently obtained observations. The eclipse timing variations of all three
pairs were studied in order to detect the mutual perturbations of their
constituent stars, as well as those of the inner pairs in the (2+2) core. At
the longest periods they arise from apsidal motion, which may help constraining
parameters of the component stars' internal structure. We also discuss the
relative proximity of the periods of binaries A and B to a 3:2 mean motion
resonance. This work represents a step forward in the development of techniques
to better understand and characterize multiple star systems, especially those
with multiple eclipsing components.
