so for testing purposes you should be able to have a 5.3 agent and connect to that from a 5.2 broker. This isn't officially supported for long term production use though - but to at least prove if the usb issue is fixed it should be fine. Specifically the fix is in the usb driver, and, the connection server does not have anything to do with usb traffic or functionality.
Right now, I can't explain why Jason had the issue he did - but lets say for testing you created a fresh vm desktop as a manual pool, and installed the agent - then that should be good enough to validate the fix....
cheers
peterB