According to ownerís manual, pag. 35, 55, 102 and 103, PSR 9000 has two Sustain features working in a different way. One is the Sustain button on panel, that add a small sustain, like a system effect, to all notes played on keyboard.
Other Sustain feature is that works using the foot pedals, that are programable individualy for each part we pretend affect.
So, with 9000 we can play Left voices without Sustain and other parts with Sustain and vice versa.
PSR 8000 (about Sustain), works only with foot pedals (it seems there is no sustain button on panel) and also itís completely programable as 9000.
PSR 740, 730, 630, 620 are not top keyboards and so, Sustain foot pedal is not programable and affects all the notes played with R1, or R2, or Left voices. Itís always like a system effect and not a insert effect.