I'd suggest also Hymnen by Stockhausen and Bohor and Persepolis by Xenakis.
But I would highly recommend exploring other composers as well. The world of electroacoustic music is pretty big, and pretty various as well. There are many composers who only do electroacoustic--Dhomont, Ferreyra, Bokanowski, Amacher, Mandolini, for example--as well as the many who do (have done) both electroacoustic and instrumental--Maderna, Berio, Nono, Varèse, Cage, Oliveros, Nelson, Mumma, and so forth.
Lots of stuff out there. Stockhausen and Xenakis represent, in all their enormousness, only a tiny fragment of the totality.