The UA-5 is not the most recent audio interface and therefore not supported by Edirol anymore. Luckily there is a Windows 7 driver available, and since newer Windows versions should be compatible, it is as easy as installing this driver – I always think. Unfortunately, that’s not working, and editing the INF file is cumbersome and requires disabling the driver signature enforcement (which is not recommended).
The solution is actually pretty simple and I found it here: Download the Vista driver, and run setup in Vista compatibility mode. This driver does not constrain the Windows version and works on all versions through Windows 10.