Holy hell I just went down this rabbit hole and it was chaos... all modern Macs use ARM processors, and you need a special version of VMWare to even use that. But nevermind, because the KLN update software only runs on Windows XP - and there is NO possible way to run that on ARM.
So I dug an old Intel mac out of the depths of hell and installed a Win XP virtual machine. Got the drivers for USB to Serial so I could try the headphone jack approach. Tried for hours to get the unit to update in that manner and could only manage to read settings but not actually write back to the unit. GPS kept saying software not ready or something.
So I ordered an ImageMate from ebay, roughly 25 years after it was manufactured. Am told by KLN software that the firmware is bad, and only Windows 98 can fix it. So install windows 98 on virtual box, drivers and all. AND THEN the firmware update software cannot find the writer even though it's very clearly installed and accessible. I start button mashing obscure USB settings in windows 98 (disabling random things that I don't even remotely understand (or care to)). FINALLY, in absolutely no repeatable manner that I could tell anybody, the software randomly recognizes the hardware.
I update the firmware without incident, then go back to windows XP and update the GPS database. And then i double fist pump the sky and scream obscenities at our simulation overlords.
What a journey - I'm 33 and cut my teeth on windows 98 as a kid, followed shortly by XP. Was quite a deep dig into a long forgotten skillset to get this procedure to work.
To the guy offering help, it is generous of you! This is quite an undertaking. Cheers and good luck to anybody else who attempts this!
