He used the PC version of Music 2000. It dates back in 2000 (the PS1 version 1999) and lacks VST plugin support, but it still lets you do some cool stuff if your computer can run it. The PC version of Music 2000 allows unlimited importing of WAV samples (hence the remixes he can create with it), while the PS1 version only allows about 4-16 seconds, depending of the quality, but the reverb effects are way better in the PS1 version.