Is there some way that I can send multimedia control commands like next song, pause, play, vol up, etc. to the operating system? Commands that are sent when pressing Fn
Unfortunately, in most cases, keys Fn can't be sent using Windows API and as a result - using .NET classes. It depends on how the manufacturer has done this functionality. Probably it is supported by additional driver or even go over operation system.
You can check if it's possible to send Fn commands from the code by trying to hook them using Windows API code or some application like AutoHotKey. For instance, on my laptop, I can't hook multimedia commands.
Otherwise, if you are lucky, use SendKeys as mentioned in the comments.