Do you notice an adjustment in volume balance between the two pickups using the German panel vs the HCT panel?
On my HCT, the bridge pickup is way louder than the neck pickup. Or, maybe it's the Bass Off function of my control panel. But when I use Bass Off, I turn the volume of the bridge pickup all the way down (off), and it's still way louder than the bass with my typical; Solo, Bass On, Treble Off setting. Plus it's a bit twangy. I only use it for a couple of songs, and even then I often hesitate and just leave the switches alone.
I also have an HCT Cavern. Do you, or any of our Hofner friends, know if this control-panel also fits the Cavern? Not sure if the Diamond pickups require a different panel. Also note, the pickups are not as hot as my other HCT and the Bass Off blends well when I use it. Not twangy
A German control panel should fit the Cavern HCT.