I have been running the beta driver for the IF-FW/DMmkII card in my DM4800 console with a MacPro 4,1 running MacOS Sierra (10.12) for several months, and never had any issues. I have been working on upgrading my MacPro 4,1 to High Sierra (10.13) today. I wanted to report that I had a strange experience when performing this upgrade from Sierra to High Sierra - BUT, it appears to be working now.
I must first disclaim that the MacPro 4,1 is not even officially supported by Apple to run these latest versions of MacOS, but thankfully there are patches online to make that work. That may or may not have played a part in the snag I had in the process of upgrading to High Sierra. The High Sierra update itself went well, but I lost the driver for my IF-FW/DMmkII. I guess I need to upgrade some hardware in the studio, but I like the tools I have and I plan to exploit them until they just don't work anymore!
Anyway, after the High Sierra upgrade was complete, my IF-FW/DMmkII driver did not load. Being that this left me in the situation of having to downgrade anyway, I tried a fresh install of High Sierra, then I loaded the beta driver (iffwdmmkii_installer_188754_release.dmg, which installs driver IFFWDMmkII-1.30f10). After the Mac rebooted, I had a warning message that said a System Extension from TEAC was blocked, and it directed me to the Security & Privacy Control Panel to allow the driver to load. Once I did that, the driver loaded and the IF-FW/DMmkII driver is loading just fine.
I'm using the DM4800 & IF-FW/DMmkII with MOTU DP8 on this older MacPro 4,1 running High Sierra 10.13, and so far things appear to be working just fine. Maybe I'll be ok for a couple more years!
-Russ
--EDIT
After fretting for a couple of hours that the control surface setup wasn't going to work, I discovered that High Sierra's new AudioMidi Setup app simplifies things a bit. For whatever reason, the DM4800 appears with only one connection point, rather than 5 or 6 like it used to. You then had to create external devices, name them Mackie Control, etc... Apparently, you skip all that and just configure things in your DAW like you normally would. But instead of pointing your Mackie control surface ports to those external devices you created and connected to the control ports on the DM4800/DM3200, you simply point them directly to the control ports themselves. I was astonished when I experimented a bit in Digital Performer and voila, control surface came right to life!
So - at the moment, I have an unsupported Mac running High Sierra 10.13 with an unsupported IF-FW/DMmkII in an unsupported mixer, and it's 100% functional. I'm living on the edge. Don't try to stop me. I'll take you down with me.