The AudioBox USB and 22VSL are compatible with UC 1.8.3
You will loose the VSL mixer feature as well as the "Z" latency functions unfortunately.
In August of 2016 we released Universal Control 1.8 which supports the AudioBox VSL series interfaces. It does not contain the VSL Software. However it will allow you to uninstall the non-functioning AudioBox VSL 1.3 software, and it will allow you to update the firmware to the latest supported version.
Universal Control 1.8 (or higher) is available on the download page for:
NOTE: AudioBox 1818VSL Remote for iPad will continue to function for previously supported operating systems where AudioBox VSL software is supported.
Please Note: With this recent change in El Capitan, AudioBox VSL users will not see the "Z" or Zero Latency feature within Studio One.
We've also created some tutorials to assist with getting your AudioBox VSL interface up and running without AudioBox VSL Software, including learning about default routing of the inputs and outputs and how to send audio to your headphones.
Lastly, if you still need to use the AudioBox 1.3 software, you can always opt to downgrade to a previously supported operating system where that software still works. We no longer provide support for AudioBox VSL software, any issues will need to be discussed in the AudioBox VSL Community forums.