Use the PC. If your music files are stored on the same computer, just use a regular music player. Try Clementine or Foobar. Both are free music players that should do anything you need. If you use Plex for other things, just leave it setup the way it is.
For cables, just go to Best Buy. They sell Audioquest. Get some entry level cables for whatever you need. They won't be expensive and you'll never have to worry about quality.
For power, get whatever your $100 or so budget will get you from either Furman or Monster. You'll be fine either way.