Awesome sounding early 90's rack system from Marshall. This comprises a 9004 preamp and 9040 power amplifier.
The preamp has two channels, clean and drive each with separate EQ and foot switchable (two channel footswitch included.) Mono send/stereo return effects loop with mix control. Stereo outputs.
For some reason only German handbook on the web: http://www.marshallamps.de/service/downloads/9004_BDA_deutsch.pdf but you'll get the idea.