Hi Floyd,
I think it may only work via a computer, I don't think there's anyway of connecting dgx 305/505 directly to another keyboard.

I midied my dgx305 via usb & my clp via serial cable to an old laptop/ running omb software.

Not sure where a pedal would fit in , though.
I think the earlier DGX's may have had proper midi ports.

best wishes
Rikki