OTOH, if it’s Excel rather than XML

you can use save your files in CSV format, import into your database as a custom table with PHPmyAdmin, and use ur001’s Docmanager class to create MODx documents. I’m in the process of transferring a database-driven site to MODx, and cobbled together a quick module to do this for news and events items, lifting some code from pkBlog. The module just reads:
include_once $modx->config['base_path'] . '/assets/modules/docConvert/document.class.inc.php';
include_once $modx->config['base_path'] . '/assets/modules/docConvert/docconvert.inc.php';
and the PHP files are attached (too scrappy to put on immediate public show!). You may be able to adapt this to your needs.

KP