Yeah, you wont hear much vocal samples in Autechre's work because to use them goes against the aim of thier work. Autechre try to remove the human element from the music completely, as if to make it seem the results of the music constructing and shaping itself or working like functions of a rhythmic machine (The "Gantz Graf" single being one of the extreme examples of that aesthetic goal). There is only a couple other Autechre tracks I know of with vocal samples in there entire works those being "Basscadet" off thier first album Incunabula and "Ccec" on Ep7, wich is thier take on glitch hop... I suppose you could argue that that's a vocal sample on "Stud" on Tri Repetae also but I think it's more likely a vocal sounding synth voice.