You can legally get DTS Sound Unbound for $0 if you know where to look. The trick is not searching for "free keys" but searching for hardware bundles, affiliate giveaways, and Microsoft Store loopholes.

You effectively get the code for $0 cash outlay. The code is "hot" because it is directly tied to your account.

While there are no universal "free" codes for DTS Sound Unbound

If you have received a code from a hardware purchase or giveaway, follow these steps to activate it: How to enable DTS-X on HyperX headphones?

Many gaming headsets include a perpetual or 2-year license that activates automatically when the device is plugged in. HyperX Headsets