The 5208 Protocol Converter provides support for "non-IBM ASCII terminals",
meaning that it supports VT100, and probably other terminal types too.
After you find out which terminals are supported, you can choose from a wide
range of emulators available for the Macintosh, or merely use a VT100 emulator
such as MacTerminal or MicroPhone II. You will also need to verify what kind
of file formats are being used, and what file transfer methods are provided by
the 5208, but one or more of the commonly used generic types of transfer
programs will likely be supported by the 5208 and terminal emulators.