I just bought a Leben Cs600x integrated along with high efficiency Klipsch Cornwall IV speakers.
I was using the 6v setting with my previous setup ( Wilson Sabrinas Jeff Rowland).
Is there a desired setting or is volume the only criteria?
I’m at .6v right now and it’s plenty loud.
Is this one of those ‘Trust your ears’ thing?
To get things straight - there is NO desired setting in the sense of one line out voltage out is better than another in all cases.
As I have written so often, there are so many external factors affecting the choice; input sensitivity of the preamp/amp, sensitivity of the speakers, size of room, preferred listening levels that a " suits all" recommendation is not possible. Why do you think dCS give you a choice?
You now have fantastically sensitive speakers (by modern standards). So if it is too loud with a reasonable position setting of the volume control at 0.6v then use 0.2v , that is why it is available
Edit: Since writing the above I have been thinking further and about using other components with your choice such as e.g a tuner or tape. They are not likely to provide adjustable output voltages. I do not want to write this as you have just purchased the Leben and Cornwalls but it seems pretty obvious to me that they are not a good match in your particular circumstances. In brief the gain of the Leben is too much if you want to keep the Cornwalls or the sensitivity of the latter is too high.