Hi...
From your description the external device sounds like the original A-Max. It needs Apple ROMS in order to function. They would be installed inside the grey box.
The A-Max card in your computer is much better, and they don't work together. The card also needs a set of Apple ROMS. I believe I've seen the software and manuals on-line for download. You can run System 7 in color using the card and proper software.
I wrote the manual for the last A-Max but haven't actually used one in about 13 years! The details are fuzzy here..but luckily there is documentation on the net!
Bob
