Hi,
easy, just download the orginal K4 factory sounds from Kawai
and use a free K4 Editor like K4Win (Just put the word into Google to find it )
to restore the factory presets.
If you want to use the K4 in one channel mode, put simply the "Omni On" to
"Omni Off" (use button "System" and "Receive" )
Greets M@rc