Looking at the G-1000 Owner's Manual, I don't see any references to being able to load new sounds. Are you talking about changing the parameters of the internal sound sets? Judging from the MIDI Implentation Chart, you can make only limited changes to the existing sounds-- for instance, you can modify the effects depths, but you can't modify basic sound parameters such as attack time, release time, cutoff, and resonance. I see something called "Source 1" and "Source 2," but I don't know what they are, and the PDF manual isn't easy to search through because it consists of scanned pages rather than searchable text.