I checked my correspondence with that original poster, and he was not able to load Synthesis in Dosbox 0.74 on Windows 8.1. That was 3 years ago. Perhaps the problem is 64 bit Windows, despite that that version of Dosbox tries to accommodate older DOS programs on 64 bit Windows (presumably including Win10).
Older Sartin programs are a problem in 64 bit environments
That's why we have the newer program
Cheers,
Ted