I'm having some difficulty figuring out how to quote comments, so
"I can’t speak to how the Leben is built, but I do know that overall it sounds better with the bottle head than with its own preamp section (alone ?). Why would Leben offer it if it would only diminish the sound?"
That's a good point - and I'm believer in 'trust your ears'. Looking forward to hearing about your further experiences with preamps with the CS-600X.