S-series samplers offer a lot more sound and program editting. Keygroups allow you to play your sample chromatic on a keyboard/midicontroller, with envelopes (attack/decay/sustain/release) for amp, filter, pan and pitch. Also, layer different samples together, loop samples and edit samples.
Basically, you can make an instrument out of short samples (even single cycle waves).
Another reason people buy those samplers is the sound. Especially the S950 (or 900) and the S3000 (non-XL) have a nice oldskool sound because of the AD/DA converters and the bitrate.
You can pick up a S2000 for about €20,- these day. I suggest you try it, read the manual and the go buy some floppydisks.
