This is my current setup: RX 580 Nitro 8GB (DP1.4) => USB Speakers (Powered by USB hub).
Initially this worked (swapping between headphones / speaker) ; however upon starting up the PC today; the monitor is no longer detected as an output device (audio). I have the USB speaker connected to port #7 as per this diagram
Here is a screenshot of my audio devices (including disabled devices - the monitor no longer shows up on this list).
PS: I've updated windows + installed display driver from Dell.com)