All of the samples come from 8Dio, so if you've heard a demo then you've almost certainly heard some of their samples in action. There are actually quite a few demos on the 8Dio Productions YouTube channel. A complete playlist with all of them is maintained
here. Here's what they have to say on the subject of what kinds of samples are included:
"The Sequential Prophet X contains over 150GB of deep-sampled instruments – derived from a wide assortment of custom libraries (specifically designed for the Prophet X) and from the 8Dio and private V8P collections. Thousands of deep-sampled instruments and far too many to list. Ambiences, Upright and Electric Basses, Studio Brass Ensemble and Studio Brass Solo Instruments (ex. Trombone, Trumpet, Saxophone etc), Large-Scale Symphonic Choirs, Childrens Choir, Experimental Basses and a large section of custom instruments.
Several deep-sampled drum kits and +50 different electronic kits, Massive Ensemble Percussion Sets, Taiko Drums, Guitars (ex. Acoustic, 12-String, Dobro, Electric, Mandolin etc), Thousands of Cinematic Sound Design Tools, Vintage Keyboards (ex. Suitcase, Hammond, Wurlitzer, Clavinet etc), Orchestral Effects. Deep Assortment of both Tonal and Non-Tonal Percussion, Grand Pianos, Upright Pianos, Prepared Pianos. Solo Voices. Studio String and Woodwind Ensembles. Custom Wavetables. Synth Ensembles and thousands of other instruments."