When you say the files are too large for WordPress, do you mean they just exceed the default 2MB WordPress upload limit set by php?
I know this doesn't directly answer your question about linking to files on a network resource from a web-accessible directory, but maybe a safer/more convenient solution can be had.
Suggestion 1. Have a server admin reset the max_upload_size directive in php.ini (or the equivalent per-site php.ini if applicable) to a size that would accommodate the uploading of your drivers to the WordPress media library.
Suggestion 2. - And my favorite choice for often downloaded content; Create a dedicated directory in your web-root just for the driver files. Example: yourdomain.com/drivers - then upload your driver files exclusively to that directory by ftp or whatever means you use, rather than having WordPress upload them to the media library. That way they become very easily manageable, and the path when creating a download link is always going to be yourdomain.com/drivers/driver_name.