I have a link in html:
<a id="clicky" href="http://localhost:8080/filesystem/IT.xls"><p>Download</p></a>
to which I would like to add additional .xls files for download. Is there a way to give a link multiple sources or to combine the sheets on the user end?
No. A link can only point at a single URL (aka resource). Nothing says that resource can’t return multiple things, e.g. all the requested files in a .zip, e.g.