xinclude mod and catalogs

I want to use the xinclude.mod to allow modular files to validate in
oxygen, but I do not want to get a bunch of warnings from xsltproc when
I build my books. I tried to use a catalog to resolve the entity
reference using:

<group xml:base="file:///c:/dcbk/custom/">
  <system systemId="xinclude.mod" uri="xinclude.mod" />
  <systemSuffix systemIdSuffix="xinclude.mod" uri="xinclude.mod"/>
</group>

oXygen likes the systemSuffix entry and xmlcatalog likes the system
entry. However, xsltproc and xmllint both refuse to resolve the entity
and throw up warnings everytime...

Any idea on what I've missed?

Thanks,
Eric J.