The manual goes into a bit more explanation about the two optional packs that were sold, a MIDI pack (Supporting SC-55, SC-55mkII, JV-30 and SCC-1) and a Speech pack. I'm not certain, but I think that perhaps one dump on the internet may already have this pack installed, it just simply needs to be called. This site talks more about it, at least how to configure it with DosBox.
[midi] # mpu401 -- Enable MPU-401 Emulation. # intelligent -- Operate in Intelligent mode. # device -- Device that will receive the MIDI data from MPU-401. # This can be default,alsa,oss,win32,coreaudio,none. # config -- Special configuration options for the device.