Maybe I can help, KainsTorment.....
Yes, you are quite right. Apple have removed the input and the output for optical-digital audio from all Macs from about 2011 or later. You'd need something with a USB-A output or a usb-C output. maybe something from Focusrite,behringer, Zoom ??,,, RME... Unfortunately, things with a thunderbolt/usb-C interface are going to be much more expensive, then ones with a a USB interface. 'tis the nature of the beast, alas. If you wanted surround sound output, that might be a bit easier to achieve, but not by a lot. The 2019 Mac Pro is still very very new, so new that support for it at your local Apple store (closed due to ongoing difficulties.... is sparse, slim, hard to find) . As for the 2019-2020 iMac Pro, it offers USB-C (thunderbolt) and USB 3.0 ports, and that's it....
Oh, and apparently, you can put PCI-E cards in the new Mac Pro. RME does make such a card, others might, I dunno for sure..... and installing it is super easy. Even easier than the older Mac Pro, the "cheese grater" model, like the one I and you, and many others have. there are 4 free PCI-E slots in it. not gonna be cheap though whichever way you want to do......
well, good luck to you
john b