The Reference 6se is excellent. My go to SS pre when I really want a hard core comparison with tubes is the SST Ambrosia Preamp. Loaded with features, it doesn't sound like tubes, yet, it does have a flare, a tube like quality, smooth, detailed, excellent soundstage and loaded with world class performance in several features.
If you like the AR Ref 6SE, I would recommend the SST Ambrosia as a comparison. Warning, the Ambrosia needs a couple hundred hours of signal passing through it for break in if new and then just leave it on. Beautiful pre that passes through the source quite honestly.