I’m planning on feeding the output from my Bartok to an Allegri+. Is there any way to lock out the volume control on the Bartok? Just so I can stop any inadvertent playing with the volume/output from the Bartok - i.e. by SWMBO 
There is a settings lock but this does not affect the volume control.
It depends on your precise concern but as the output from Bartok to Allegri should be set at 0.0dB SWMBO could only turn it down and not up past the optimum setting.
Oh I agree but I’d rather set it once and forget and not have to keep on rechecking it all the time when I come to play something