Rendering XREF's

Hi, I have a problem with Autocad.I have created a large suite of
"symbols" as XREF's. I attached materials to these symbols, such as
timber and metal.
Trouble is, when I import these XREF's into my master file, I don't
see the materials. This means I must laboriously BIND or EXPLODE my
XREF's, and re-attach materials.
Is there a better way of doing this?
Kerry