  We present results from four new broadband X-ray observations of the extreme
ultraluminous X-ray source Holmberg IX X-1 ($L_{\rm{X}} > 10^{40}$ erg/s),
performed by $Suzaku$ and $NuSTAR$ in coordination. Combined with the archival
data, we now have broadband observations of this remarkable source from six
separate epochs. Two of these new observations probe lower fluxes than seen
previously, allowing us to extend our knowledge of the broadband spectral
variability exhibited. The spectra are well fit by two thermal blackbody
components, which dominate the emission below 10 keV, as well as a steep
($\Gamma \sim 3.5$) powerlaw tail which dominates above $\sim$15 keV.
Remarkably, while the 0.3-10.0 keV flux varies by a factor of $\sim$3 between
all these epochs, the 15-40 keV flux varies by only $\sim$20%. Although the
spectral variability is strongest in the $\sim$1-10 keV band, both of the
thermal components are required to vary when all epochs are considered. We also
re-visit the search for iron absorption features, leveraging the high-energy
$NuSTAR$ data to improve our sensitivity to extreme velocity outflows in light
of the ultra-fast outflow recently detected in NGC 1313 X-1. Iron absorption
from a similar outflow along our line of sight can be ruled out in this case.
We discuss these results in the context of super-Eddington accretion models
that invoke a funnel-like geometry for the inner flow, and propose a scenario
in which we have an almost face-on view of a funnel that expands to larger
radii with increasing flux, resulting in an increasing degree of geometrical
collimation for the emission from intermediate temperature regions.

High Energy Astrophysical Phenomena;Astrophysics of Galaxies