Ok so here is some basic knowledge.
DAC: Digital to Analog Converter. This tool converts digital files (bits, bytes, ect) into analog (sine wave) and then pushes that analog signal to some sort of amplifier.
Based on what you said you really want is a portable source. Any of the DAPs listed will work. There is probably something you could use that has no Gui that you just plug a USB stick into and it reads the files and plays them in order.
Take a look at DAP - Digital to Analog Players. iBasso, Sansa, Fiio, ect are good manufacturers to start with.