The short answer is no; there aren't currently any XLSX reading modules in Perl 6 (at least not that I know of).
However, do you really need to be using an XLSX format? If you could switch to using tab-delimited or csv-formatted files, I'd recommend that. I'm surprised by how often complicated formats are used for very simple data.
But if you must use XLSX, then I'd recommend using Perl 5 with one of its well known and well tested modules.
But if you must use Perl 6, then here's what little I know:
For writing files, the XLSX::Writer
Perl 6 module that you mention is "a wrapper for the libxlsxwriter C library", which just writes XLSX files, but cannot read them.
For reading files
a. You might try using XLSX Perl 5 modules via Inline::Perl5
.
b. You could try creating a Perl 6 wrapper for a C or C++ library such as XLSX I/O or xlnt.
If you come across or create a Perl 6 module that reads XLSX files, please post that information as an answer to your own question and notify me via a comment.
Text::CSV
in a native Perl 6 version. – Tragedy