All functions work with fully free software, including MIDI i/o, 2x capture, 2x playback, SPDIF output. Format is locked at 48000Hz @ 24bit.
However you need to upgrade its internal firmware once before use.
You need to upgrade your Mbox 2 firmware to v1.43 using the official updates provided
here, also mirrored on ZamAudio
here.
Without the update, strange noisy inputs occur with the Mbox 2 on GNU/Linux but when the update is applied once, the noise disappears.
The firmware update can only be applied from a Mac or Windows computer.
However, once firmware update is applied, it works with any Linux kernel >= 3.14.
To inspect your current firmware version:
sudo lsusb -vv -d 0dba:3000 |grep bcdDevice |awk '{print $2}'
Anything less than 1.43 needs an update to 1.43