Apparently on my previous tries, I must have had an error of some sort. Thanks now to @daneover and the great step-by-step guide they provided, I'm now listening to some tunes on YouTube, via my Mackie Onyx-1220i 's Firewire connection!! Mac mini 2023 with M2 Pro | 32GB RAM MacOS Sequoia 15.6.1 Followed the instructions in sections 1, 2, and 3. No apparent issues installing the FW kext from the AppleFWAudioVentura.pkg. Downloaded the ZIP file & extracted the .pkg to my desktop. Note: One thing I did not do is have the Mackie connected to my Mini via FW during the whole install/config. I waited until the last step in part 3 (after double reboot) to finally get connected. Also of note, I have had success via 2 different ways to connect to my Mini. In previous attempts, I tried the "dongle daisy chain" method with a FW800 (male) > FW400 (female) adapter connected to the Apple FW800 > TB2 adapter, and finally the TB2 > TB3 adapter. This time around, that collection of adapters is working great. Prior to buying the Mini M2 Pro, I was deeply involved in the "Tonymacx86.com CustoMac" community, and recently uncovered an old Belkin F5U504 - FW400 3-port PCIe card - just like this one... https://www.hardwarejet.com/belkin-f5u504.html?srsltid=AfmBOor77YlzKP4ebugD3tNbx-x0UfVNRgtuCS5Cn1GMU4hNTsPrrDcY, along with my Blackmagicdesign Intensity Pro 4K video capture card that were running successfully in my most recent "hack-intosh." So Friday I found a reasonably priced Thunderbolt 3/4 PCIe enclosure on Amazon (search Amazon for ANQUORA Thunderbolt External Enclosure TD1). Popped the Belkin card in the enclosure, connected power & TB4 cable to enclosure, and finally connected my FW400 cable from the Mackie to the Belkin card. BINGO! Again, beautiful (no snap/crackle/pop) audio playback. Have yet to test recording using the mic inputs, but I have no reason to suspect any issues. For now, my Mackie mixer lives to fight another day via Firewire! Again, huge thanks to everyone who's chimed in on suggestions, troubleshooting, and to the folks who meticulously documented the process.

Just curious if anyone has this working on MacMini M2 Pro with Sequoia? I, too, have a Mackie Onyx 1220i and am really missing the FW support! TIA!