polaroid,
No, I'm afraid you can't - these synths use small sampled waveforms stored on ROM, but a user cannot download new waveforms. All sounds you can get out of the synth are based on layers of these basic waveforms, then put through the typical functional blocks of a well-specified analogue synth. Finally, there are also two basic multi-effect sections.
When you buy a sampler, or a synth with sample-playing capability, you effectively pay for lots of RAM and a load of onboard software which offers sample management and comprehensive editing facilities as well as a more complex user interface. Also, on a dedicated sampler, you have a line input, ADC and usually some interface and support for disk storage.
A moderately complex synth OTHO can be implemented on a single chip, which is much cheaper.
Jim
