Thanks for double-checking on cables and sorry to hear this didn’t help. As I’m sure you know, the behavior you describe is both unique and unexpected- thanks for your patience as we troubleshoot.
As we dig in it would be helpful to know exactly which model of USB graphics device you have- or you can just shoot an email with your Amazon order ID to firstname.lastname@example.org with a link to this thread and I can look it up.
Next, I’d like to make sure I’m understanding how everything is connected and try to rule out any potential USB power related issues. If I’m understanding correctly the USB graphics adapter is connected directly to your MacBook Pro (MBP) and you’re also connecting the external speakers via a “headphone” style 3.5mm auxillary audio cable (not USB?) directly to your MBP. Please let me know if any of that doesn’t sound right. I’m wanting to understand more about the speakers (these are separate from the monitor?) and how they’re connected.
I’m hoping that we might resolve the issue by making sure all the USB devices have adequate power, so double-checking that any hubs are powered properly could help.
If you can share a little more detail about the particular devices involved (model numbers are most helpful) I’m hopeful about finding a quick fix by changing connections, and if we can’t find something quickly that way we’ll be glad to try swapping out a pre-tested replacement to rule out faulty hardware.