Inside The Chemical Brothers Stage Performance: A Behind-the-Scenes Look with Matt From Gravity Rigs 

Ironically, the sound quality in this video is awful

They can tweak and embellish the backing tracks with the gear tho. Add some spontaneity to the performance

Yep, they have two laptops with Logic Pro X, it runs all the main stuff like playback stems and all the MIDI, both laptops synced simultaneously through Sync-Gen II hardware or something like that, both laptops generating same audio/midi signals to separate MOTU interface cards and those signals went through Radial SW8 units, that can switch the signal from one card to another. I.e. from one instance of Logic to another. Logic is also generating SMPTE signal, that goes to light and video teams to be in sync. There's also a laptop with Ableton Live to play "one shot" samples from "Drum Rack" that are triggered by Ableton Push controller and many others now. Also i guess Ableton now is loaded with a bunch of VST/AU plugins that should cover failed synth on a stage. And of course Ableton is a host for Maschine, that is loaded with a lot of loops with drums and track parts that Tom is triggering during the show. It's a big complex, difficult, archaic, but it works.