Hi Ralph,
For General MIDI (GM) it's true that the default drum channel is 10, and so if you're only using one device you're sort of stuck with just one drum staff/channel.
However, if you have a MIDI playback device that can assign different channels (eg. Garritan Personal Orchestra, or other library or device) then you can set a different channel for the drums. Alternatively, if you have multiple devices (eg. VST Host, and use multiple instances of SynthFont), then you can have multiple Drum staves (some hidden, as David suggests) and assign each one to a separate device.
There are lots of ways to be flexible, but it does add a bit to the complexity factor
If you're using your Clavinova to do this, then you may well have the inherent capability to set different banks of drums via different channels. You can check the user manual for the Clavinova to see.
ttfn,
Sherry