Magellan nav systems seem to require a unique name for each POI.
When you import from CSV format, POI File Editor discards any location if the name matches one that's already been imported.
The red light cameras file has unique names and imports easily. Other files, however, may need to be modified before importing to avoid duplicate names.
So far, it seems Magellan nav systems can only use their built in alert sounds.
There does not seem to be any way to set alert sounds that use custom MP3 files.
Microsoft Excel can read .csv files, but so can many other programs. When Excel is installed on your computer, it automatically associates the .csv extension with Excel. This is why the files show with an Excel icon.
If you look closely at the icon, you'll notice it's slightly different than the icon that's normally used for Excel spreadsheets / workbooks.