Aminet's search is fairly old-fashioned, but very powerful in its precision. The default simple search only does exact matches in the filename or description, so it's best to be as general as possible, e.g., "ixemul" rather than "ixemul.library".
As RhoSigma says, you can hunt much more deeply with the advanced search. "Readme" searches for an exact match in the full text of the readme file, "Contents" does the same for filenames within the archive. Those fields are really helpful for including the contents of, for example, the Fred Fish disks in searches, which almost never turn up otherwise.
