You are probably talking about USB Audio, it was actually added earlier in 4.1. The device also has to support USB Host. S4 does support USB Audio. The biggest problem is that Google does not give a damn about compatibility with external accessories. As far as I understand not all external USB Audio DACs/cards are compatible with all USB Audio Android smartphones.

EDIT: Here is what I think should work. Disclaimer: I'm not absolutely sure about compatibility.

• This cable. Male micro-usb goes into the phone, female micro-usb to the power, female usb to the audio converter.
• USB Turtle Beach Advantage Micro sound card

EDIT2: This thing may potentially work too. It says "USB Audio Device Class Specification 10" so there is hope. Buy it at your own risk.