Why has Moog not made a very simple and quick modification in the Etherwaves since Melodia until today? A mystery to me. A proper reduce of the coupling leads directly to a playability of a very deep string bass.
It's meant to be a benefit, see 'Hot-Rodding your Etherwave': "C2 and C6 also provide weak coupling between the two pitch oscillators, which has the effect of synchronizing the pitch oscillators when their frequencies get very close together. This has the desirable effect of providing a stable 'zero beat', so that the instrument, once properly tuned, is silent when the player steps away from it".
Which besides explains why there is no mute switch.