As I'm sure you are aware, when you select the KN7000 Split Keyboard option, it kind of simulates a dual manual keyboard, with independent sounds above and below the Split Point. Technics in their wisdom, also added two extra sounds below the Split Point - The CHORD sound and the ROOT BASS (R.BASS), which help to fill out the left sound, when played without the APC operating. Both the CHORD and ROOT BASS sounds are under control of the user and can be changed, just like any of the other sounds. Both of these sounds cease to operate as soon as you start the APC playing and resume when you stop the APC.
You can disable the CHORD and R.BASS sounds by turning off the APC mode - Press the APC button - the LED turns off. If you select the Left sound ON by pressing the LEFT button in the 'Part Select/Conductor' section, you can have independent sounds in all three Parts (Left, Right1 and Right2), without the CHORD and R.BASS sounding. You can even use the Technichord in this mode. If you turn off the LEFT part, then the keyboard reverts to a total single sound, determined by the selected sound in Right1 or Right2 or both together.

The CHORD sound settings can be changed as I described in the post above - both actual Sound and Volume - but there is another way to change these settings.......
Press Program Menus Button > Sound > Mixer > Other Parts button TWICE, and the Mixer screen will display the settings for several of the available sounds. On the Right Hand side of the display, you will see settings for Bass Pedal, R.Bass, Chord, Left, Right1 and Right2. You can alter the setting for any of these six sounds. For example - to change the sound used in the CHORD, press the Top Left Screen button to highlight the 'SOUND' section of the display (Orange Bar moves) and then press ONCE, either of the two buttons below the CHRD slider on the the display - the currently selected sound for the CHORD will be highlighted. You can change the sound by either selecting one of the Sound buttons in the 'Sound Group' - the screen, will change to allow selection of the new sound, and then auto-revert to the Mixer display. You can also step through all the available sounds, by just pressing the Upper and Lower buttons below the CHRD slider.

Having selected a new sound, you can then set the Volume to your liking. Press the Fourth button from the top, on the left of the display, to highlight the Volume Section (Orange Bar moves) then use the two buttons below the CHRD slider to adjust the Volume. If you wish to mute the CHORD sound, then either set the Volume to '0' or press both buttons below the CHRD slider simultaneously - a small 'MUTE' icon will appear over the slider. Pressing either of these buttons again, will remove the Mute setting. The above procedure can also be used to change the settings for other parts, which are displayed on the Mixer screen - for example - the R.BASS sound and Volume. Note that loading other setups from Panel Memories or SD Card, will overwrite the settings for the CHORD and/or R.BASS which you have just made, and will reflect the sound settings which were present, when the SD card file was saved, or the particular settings in the Panel Memories.

However, you can use the CUSTOM PANEL facility, to store your new settings - including the muted/changed CHORD sound if you wish - and this will allow you to recall your new settings at any time, by just pressing a single button, instead of going through the above procedure. The settings in CUSTOM PANEL are retained through Power-down, since they are stored in Flash Memory. First, you should configure the CUSTOM PANEL mode as follows.... Press the CUSTOMISE button (Lower right corner of the panel) > Custom Panel Mode > select 'ALL PANEL' > OK and then press the EXIT button twice.

Having made your new Sound settings, Press and HOLD the blue 'SET' button in the middle of the Panel Memory group and then press the 'CUSTOM PANEL' button just to the Right of the Panel Memory group. This action will store your new settings for the CHORD / R.BASS sounds and you can recall this particular setup at any time, by just pressing the 'CUSTOM PANEL' button, once.