MixEmergency is a plug-in application for Scratch Live - this means that any hardware that Scratch Live supports for audio output (i.e. SL 1 and the TTM 57SL) will work with MixEmergency. The TTM 57SL is a special case though, as MixEmergency also reads the fader positions (crossfader, cuefader and upfaders) for use with MixEmergency's faders. If you have a TTM 57SL then you do not need a SL 1 connected. But, as I wrote before, currently you cannot assign any of the TTM 57SL's other controls (i.e. EQ/buttons) to any of the other functions in MixEmergency - which is something that you could do with a MIDI enabled mixer. You can still use a separate MIDI controller to control MixEmergency's effects/transitions/etc though.