If I understand correctly, the thumb drive contains music files, so you are looking for a DAC into which you could plug the thumb drive? DACs will typically have RCA (and often XLR) analogue outputs, so that part shouldn't be a problem.
At the very simple end of things, something like the Allo Katana would let you plug in a USB thumb drive with music files and use a computer/tablet/phone on the same local network to tell the Katana which music files to play. It has a RCA outputs that would send analogue out to your amp/preamp. Since it is based on the Raspberry Pi computer platform, it can use Volumio or MoodeAudio software that lets it see the music on the thumb drive and play it back. You can have one of those preinstalled by Allo.
https://allo.com/sparky/katana-player.htmlThere are more expensive options as well, like the Bluesound Node or the Lumin D2
https://www.luminmusic.com/lumin-d2.htmlFor convenience, you could put all of your music on a USB solid state drive (more capacity than most thumb drives) and have everything available for playback.