GM/GS synth in Roland's Sound Canvas series. With the SC-55 Map enabled for all parts it sounds quite comparable to a SC-55, yet natively the SC-88 has higher instrument quality and additional instruments & effects. Some games (and MIDI files on commercial collections like Nihon Falcom's) were produced using the SC-88.

Useful things

Sysex commands

GM reset: amidi --send-hex="F07E7F0901F7" -p hw:1,0,0
GS reset: amidi --send-hex="F04110421240007F0041F7" -p hw:1,0,0

Factory reset

Hold reset and press Intrument L/R buttons simultaneously.

Setting OUT/THRU to THRU

To passthrough MIDI data via the OUT/THRU port, you have to set it to THRU. (default is OUT)

Press Up/Down simultaneously (labeled SC-55 Map & EQ) to open the parameter menu.
Press Up or Down to select "%OUT/THRU:".
Press Instrument R to set it to "THRU".
Press Up/Down again to confirm.
Power cycle for the setting come into effect.

This will work fine without a battery in the unit. If the unit is powered off for a while you'll need to do it again however.

If it's not working, make sure you're using IN A for the data you want to passthrough (although it is possible to change settings to passthrough IN B instead), and that the PC switch is set to MIDI (needs power cycle to take effect).

Passthrough is particularly useful to combine the SC-88 (& Pro) with other synths like the MT-32, or a machine running munt. Connecting the device additionally to the INPUT audio ports of the SC-88 allows you to leave everything connected and comfortably toggle between the two synths by muting one or the other.

MIDI reset

GS reset: hold select and press Instrument R
GM reset: hold select and press Part R
CM64 reset: hold select and press Instrument L