Jerry W. Lewis wrote:
1. The two approaches are mathematically equivalent, provided the variances
and covariances are estimated compatibly in the two approaches.

I would never have guessed. (Well, perhaps I should have.) But....

your empirical difference is likely due to Excel's COVAR()
function being misnamed--in the naming convention of the VAR(), VARP(),
STDEV(), and STDEVP() functions, COVAR() should be called COVARP()

Bingo! When I switch to using STDEVP(), just for "proof", the results
are indeed identical. Thank you very much!

To calculate a covariance analog of VAR() and STDEV(), use either
=COVAR(xdata,ydata)/(1-1/COUNT(ydata))
or
=CORREL(xdata,ydata)*STDEV(xdata)*STDEV(ydata)
The first approach is simpler for your application, since the correction
factor would be the same for all covariances.

Yes, but the latter is similar to an alternative mathematical
formulation; and I do have the SDs of the individual asset classes.
Ironically, the Correl() formula is what appears in the literature.
Perhaps now I know why ;-). I shot myself in the foot by "simplifying"
the equation, reducing it to Covar().

2. A simpler approach would be
=SQRT(SUMPRODUCT(A5:A11*TRANSPOSE(A5:A11)*B15:B21) )

After correcting the last term to B15:H21, it works great. Thanks
again! And I was able to do the Correl() formulation similarly,
namely:

=SQRT(SUMPRODUCT(A5:A11*TRANSPOSE(A5:A11), N5:N11*TRANSPOSE(N5:N11),
K15:Q21))

where N5:N11 are the SDs, and K15:Q21 are the CORRELs.

Thanks again for your insights. And Happy New Year!