Chas,

I use both a sustain and a volume pedal on my S900...although I feel the sustain pedal is more important and always carry a spare.

"Riding" the expression pedal always adds so much to organ...velocity sensitivity actually feels(and sometimes sounds) unnatural to me, although I can get by without the pedal if necessary as the organ sound on the S900 fades away when using the sustain.

For solo piano...the sustain is a must...for solo organ (or in a combo) the expression/volume pedal is a must.

Ian