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Download the Universal Audio Installer and Universal MIDI installers appropo for your OS. In the drop down menu for the Audio, you can install the PCI, USB/FW or both for the audio.
This will not include Audio Desk. If you need it and your unit shipped with v.1, the current version is a paid upgrade - you also have an upgrade path to DP (Mac and Win). If you have Audio Desk 2, you can upgrade to 3 with your current serial number found in your manual. Audio Desk is also in the Downloads under software.
If you obtained your unit used without a manual, you can find it on MOTU.com (it may not be v.II but it will get you going). It won't have a serial number for Audio Desk, of course.
BTW, I'm not certain that you need the Universal MIDI installer with the 2408. I have a MTP AV so I install them. If you are not using the MIDI port, then you don't need that installer, of course. Perhaps someone who knows more about this than I will weigh in on the subject.
DP 11.34; 828mkII FW, micro lite, M4, MTP/AV USB Firmware 2.0.1 2023 Mac Studio M2 8TB, 192GB RAM, OS Sequoia 15.4, USB4 8TB externals, Neumann MT48, M-Audio AIR 192|14, Mackie ProFxv3, Zoom F3 & UAC 232 32bit float recorder & interface; 2012 MBPs (x2) Catalina, Mojave IK-NI-Izotope-PSP-Garritan-Antares, LogicPro X, Finale 27.4, Dorico 5, Notion 6, Overture 5, TwistedWave, DSP-Q 5, SmartScore64 NE Pro, Toast 20 Pro