Thanks for the replies everyone, this is most helpful!

There are quite a few things that are slightly over my head within this
field, as I'm trained (training?) primarily as a musicologist.  As a
thesis in music history, I'm investigating methods of encoding musical
manuscripts / printed sources within a digital collection.  So, for
example, if you had one of Bach's manuscripts, it is interesting both
from an archival and a musical perspective.  From the archival
direction, the current libraries holding it, the collection it is in,
physical state, etc. are all important pieces of information for a
researcher.  As well, the actual music from a bibliographic point of
view is important - what instruments are in it, what tonal / modal
system does it use, who's the composer / lyricist?  The actual notes
are secondary to the bibliographic information - theoretically there
would be a picture attached to the description.

The problem facing many music researchers is that music, especially
pre- and early-baroque, is spread globally.  One library in Venice
might have one piece, while a small church in England might have
another piece by the same composer.  From a researcher's point of view,
if they were able to have access to all the information on a piece from
"the comfort of home", it would help them immensely.
It's also important when one realizes that, no matter how good our
preservation techniques are, these records are fragile and prone to
disintegration over time.  If we can find a proper way to encode the
information on each of these records, including photographs of the
originals, it would allow us to preserve them as closely as possible.

Defining what is "Archival" and what is "Bibliographic" might be a good
way of doing it now, but looking down the road, there needs to be a
point of convergence - a point where a document is recognized as a both
a member of a larger body, and as information unto itself.  I am
enjoying Bill's comments, especially those of expanding EAD past
Archival usage and into the bibliographic world.  Its strengths are
that it is a defined structure which maintains hierarchical
relationships, and allows physically separate items to "appear" as a
single collection. (in theory, at least.)  If only there were some way
of actually describing the stuff within the collection.

On a more technical note, I'm not sure if you can mix standards within
one another.  For instance, in a <c> tag within EAD, could you, for
instance, place a <performance> tag taken from the TEI?  A thought that
just occurred to me: Nested Schemas?  Could I, for instance, define a
section as TEI, and then define the next section with, say, MusicXML?
Or define a TEI section WITHIN a MusicXML section WITHIN an EAD
document.  All with validation and/or corresponding DTD's.
  Like I said, I'm new at this, so if my understanding of these things
are a little off, please correct me.

Too many questions!  I'll stop now. Thank you for the discussion that
has been generated thus far.

Acadia University