  We present a new treatment of two popular models for the growth of structure,
examining the X-ray emission from hot gas with allowance for spectral line
emission from various atomic species, primarily ``metals". The X-ray emission
from the bright cluster sources is not significantly changed from prior work
and, as noted earlier, shows the CDM$+\Lambda$ model (LCDM) to be consistent
but the standard, COBE normalized model (SCDM) to be inconsistent with existing
observations --- after allowance for still the considerable numerical modelling
uncertainties.
  But we find one important new result. Radiation in the softer band 0.5-1.0keV
is predominantly emitted by gas far from cluster centers (hence ``background").
This background emission dominates over the cluster emission below 1keV and
observations of it should show clear spectral signatures indicating its origin.
In particular the ``iron blend" should be seen prominantly in this spectral bin
from cosmic background hot gas at high galactic latitudes and should show
shadowing against the SMC indicating its extragalactic origin. Certain OVII
lines also provide a signature of this gas which emits a spectrum
characteristic of $10^{6.6\pm 0.6}$K gas. Recent ASCA observations of the X-ray
background tentatively indicate the presence of component with exactly the
spectral features we predict here.
