How to start streaming

Hi you cannot stream files wirelessly straight to the DAC you need to connect the DAC to a device that can stream. That could be a streaming device or a computer. The Gungnir itself is simply a DAC not a streamer and has no wireless capabilities. If you do a search there are tons of recent informative threads here about streaming to get you started.

You say you have “ a large collection of such files on my PC and external hard drives which I have converted to CD”. I guess I confused as to what that means?
jond is correct, you need a device that can stream. There are dedicated streamers by many audio companies now and you can use a computer as well. One thing to keep in mind, if you are using your new DAC as an alternative DAC to the one in your CD player and wish to use it also with a streaming device, you will need a device to switch it, like a preamp or coax/usb or optical switcher.
Perhaps some here, who use an external DAC with both a computer and CD player can offer advice if you are using a CD player.