I owned a Leben CS-600. Great integrated amplifier. I used a Purist Audio Dominus Ferrox power cord with excellent results.
If I owned a CS-600 today, I'd also try a Oyaide Tunami GPX. Terrific cord for a very reasonable price. I believe there's a used one listed now for under $200 (I have no relationship with the seller).
However, as Foster_9 already said, there is no correct answer. You'll have to try several and select the one you like. You'll know it when you hear it.
If I owned a CS-600 today, I'd also try a Oyaide Tunami GPX. Terrific cord for a very reasonable price. I believe there's a used one listed now for under $200 (I have no relationship with the seller).
However, as Foster_9 already said, there is no correct answer. You'll have to try several and select the one you like. You'll know it when you hear it.