This might be too general of a question but I’ve seen lots of bookshelf speakers that have built in DACs which connect to the PC with USB.
Do these generally work in Linux? Are they usually a standard audio device?
I’m not going to @ anyone if I buy one and it doesn’t work in EOS.
It’s essentially the same thing as an external DAC, just built right into the speaker — much like a USB headset. For example, I have a dedicated external DAC (Fiio K5 Pro) connected to a USB port, with my speakers plugged into that. It runs out of the box. So, everything is fine.
The Fiio stuff is easy to check if it will work in Linux though. The speaker manufacturers make no mention of what OS they support. The kernel is going to need to support the device isn’t it?
Welcome btw! 
In the ten-plus years I’ve been using Linux, I have never encountered a situation where a necessary driver or support wasn’t available in the Linux kernel—except perhaps with very new hardware, but that’s hardly the case here.
I’ve used both iFi and Audiolab dac’s without any issue, both have just been plug n play.