http://www.bigbookofamigahardware.com/bboah/product.aspx?id=340
AMax has 1989 Copyright stamped on its PCB which is way earlier. Amiga and ST weren't real computers though, didn't you know?
I could not find a release date for MagicSac/Spectrum on the Atari ST but I know they did create a Macintosh emulator for the ST first. Amiga folks may not know this but it is one of the reasons we got A-Max.
The programmers who did MagicSac/Spectrum on the Atari tried to port it to the Amiga and failed. They basically got a very slow, limited memory (64k?) emulator that on ran in Chip Memory. They announced (via Usenet I think) that they had given up and said the Amiga was not capable of having an emulator given its OS, custom chips, and memory configuration.
Simon Douglas thought this was crap and decided to write one himself. Over a weekend, he had the Macintosh boot screen up and running. It took longer for the other drivers and polish but he ended up creating A-max.
You purchased A-max, a set of Mac roms, installed them in the external box, and plugged it in. Poof! A working Mac emulator (you could even allocate the 256k Kickstart memory!)
It was also incredibly easy to dump the roms to a file, load them into the correct memory location, and then patch A-max. A full Mac emulator on one floppy disk. :-)
I was able to talk with Simon Douglas at an Amiga show -a long time ago- and he spoke in great detail about the development of A-max.
Emplant took up the mantle from A-max and did a multitasking Mac emulator.
Not to be outdone, Amax IV was released with very similar features.
Both great products and great designs. Though I bought and used Emplant for college so I do not know very much about Amax IV. However, I wish I knew what happened to Simon Douglas...seems like he fell off the planet.
Jim Drew has written much about Emplant, UU, and showing his product off to Apple. It was pretty cool to show people your Mac emulator running right along side your Amiga back in the day. Good times!