It’s the way to add Millennia preamps to your Dante network. Any HV-3R ever made can have this option installed (digital option required). RedNet compatible
Dante Interface Cards are also known as Dante Option Cards. Audio equipment is often designed with card slots to increase the flexibility of their device. The slots allow the user to buy and install the specific capabilities they need, and update as technology changes, without having to replace the entire piece of equpment. For example, many users started replacing CobraNet and other I/O cards with Dante interface cards when Dante became the most popular audio networking technology.