[Apollinaire]

I am not OP, but I received a used Mbox 2 Pro today and managed to get it running on macOS 10.13.4 High Sierra. I will describe what I did in order to get it working:

First, I plugged in the Mbox 2 Pro and then installed the Legacy 10.3.3 driver. During installation, there was a security alert saying that I needed to approve the driver in System Preferences > Security & Privacy. I opened it and pressed the button that appeared there to approve the driver. The installation continued after a couple of minutes, and then the system restarted.
Now, this is where I was briefly disappointed: the Mbox 2 Pro appeared in System Report under Firewire, but it did not appear in the Preferences panel, nor MIDI Audio Setup.

I figured that perhaps because I plugged it in before driver installation, or that perhaps because of the security interruption during installation, these actions may have caused an issue. So I did the following:

1. Unplugged the Mbox 2 Pro from Firewire.
2. Deleted the Digidesign Mbox 2 Pro preference pane from System Preferences (right-click to delete).
3. Ran the Mbox 2 Pro 10.3.3 driver disc image and re-installed the drivers. System Preferences did not interrupt with a security request this time.
4. Once the installer restarted the MacBook Pro, I plugged in the Mbox 2 Pro right when it went dark, before the startup chime.
5. Mbox 2 Pro lights came on, it appeared in Audio MIDI Setup and I was able to configure to 24/96. Working beautifully!

I hope this helps you with issues. I am very happy I worked it out because I won my Mbox 2 Pro in an auction for 99¢.