How do I get my mp3s from my hard drive to my speakers?

With my system, I was able to add my songs from my hard drive to my Spotify account. My Marantz ND8006 CDP has a Wifi streamer with a decent DAC. So I stream from my iPhone to the Marantz. Works for me and sounds excellent, Hope this helps.

Good idea if you have a Spotify account.  Once you move up to lossless a streamer is recommended.

I am missing something here.  Why can’t he connect the computer to the DAC and use iTunes or Windows Media Player or whatever he has to play the files?  I haven’t played files from a computer for a couple of years but that used to be the drill...

You don't need an additional player or hardware. You need a program or software like itunes, jriver, audionirvana, foobar2000 and so on. See what mahler123 said.