Hi,
and if you cannot export a media, you could decrease the catalog protection for a specific old media. To get a fast import when it comes to restore, I recommend to copy catalog to file for a specific media (omnimm -copy_to_mcf ...).
I also recommend to run a purge of filenames (use -force option) and defragment the IDB afterwards with export and import of IDB. This schould empty some space and fnames.
Please plan for uprade to newer DP version, as the old IDB limits are no longer valid with the newer DP versions.
Best regards
Daniel