Arma 3 just seems to grab hold of the standard sound device and then doesn't let it go since the 1.58 patch.
There is no settings option to change the sound device and when I use external software like Pavucontrol to try to force-switch the sound device, Arma just immediately switches back.

For most people this is probably not an issue, but I have a seperate sound device for my headphones (an E18 dac), while my other sound device (3.5mm onboard sound) is used for other things.

The only way to change it is by externally switching the standard device, which can result in external conflicts.
Before the port was updated to 1.58 I could manually force Arma 3 to use the non-standard sound device.