Hardware manuals

Steinberg MIDEX & MIDEX+ manual - Courtesy of NCGM
Documentation on Atari ST/TT series hardware - Courtesy of Neo Bechstein (Site and documentation is in German)
Scanned manuals, guides and miscellaneous documents - Courtesy of Datavase (aka atarisince1989)
Steinberg FDI manual - Courtesy of NCGM
Steinberg SMP24 manual - Courtesy of NCGM