First, does your monitor have an audio output? Some do, and it will output the audio from the HDMI/DisplayPort input.
If not, you could get an HDMI audio extractor (like this one) to split the audio out of the HDMI signal. Then you can get any streaming device that has an HDMI out.
If your speakers are not powered and you are not married to your amplifier, you could buy an A/V receiver.
The PB&Js your mom made and cut into quarters diagonally and brought out to you and your friends playing in the backyard when you were six. The ones with the toothpicks in them, indicating they have crunchy PB. Best after sitting for ten minutes so the jelly starts to leak into the bread a little bit. With a glass of milk.