@rj-schneider
I thought I had responded earlier but don??t see it.
If I understand your question, you want to view geoid data files. Your message does show that in addition to spreadsheet files (xlsx) data is available in the KML and shapefile formats.
There are open source packages like QGIS that accept both KML and SHP.
While not quite acknowledging that ??resistance is futile?, I find the Google Earth package is a good viewer for data.
I never liked spreadsheets preferring my data in comma-separated plain text in order to import into tools like Matlab. I have never devoted much time to developing spreadsheet expertise. I understand that the Open Office software package includes a spreadsheet tool.
Good luck,
DMM