Illustrator 8 format does not support many of the "live" effects and transaparancy effects featured in Illustrator versions 10 or later.
One possible work-around might be saving the file as a PDF. That may help on reducing the huge file size associated with trying to save any raster based content.
Outside of that, I would try saving the vector portions only of the document in legacy Illustrator 8 format and place the other raster-based stuff separately in whatever other application you're wanting to use for importing the artwork.