Leben CS600 owners, what tubes have you rolled?

Neil,
On my setup, the Reflector 6n3ce tubes are very well balanced tonally and are the exact replacement for the 6L6GC as far as setting go. If you are using Sovteks now you will notice a much more smoother treble and midrange and the same bass slam as you are used to.
I have heard the SED 6L6GC and not the RCA black plates and the reflector is far better.For the price the reflector option seems like a very good bet as they are not expensive..you can always keep it as a backup.

Another option is the Tung Sol KT120. I still am awaiting mine to roll to see the difference but they are supposed to be much better (let me check to see where it is better and by how much)

OK. I have the KT120s running past the 20 hr mark and they are outstanding. especially around both High Freq And Bass
the first 1 hr they were horrible and the treble was almost screechy..but then it started opening up.
the articulation in the bass as well as the clarity in the highs really standout, I believe the 6n3ces have a great Midrange as well so i am not able to notice too much of a jump there..but in a couple of days will put the 6n3ce back just to see the difference
At this point they are a big thumbs up....and you can safely upgrade and give the 6n3ce's a pass.

After more than 2 weeks i must say these tubes shine. and when i put on the reflector After getting sued to this the music seems to have gotten Duller (relatively speaking as i used to love this before)
I would wholeheartedly recommend them over the reflector (next best) and the SED (after both of the former...not having heard other 6l6's)
The Bass is so much more articulate and the double bass is to Die for (Kings of bass- Gary karr, Ray brown - producers cut) the lower end harmonics have never been more clearer...and with no loss of midrange purity. I played the Chesky's ultimate demonstration disk yesterday night and was in raptures during Ms Pidgeons voice...which is not my usual favourite.
Bolero, the dumper tube has no sonic impact (or so i believe) as it only regulates the current initially so as to preserve the life of the power tubes. so would not have any impact
I really dont know enough about the KT77..they would be good no doubt.

Regarding Leben sound, from my personal view, the tonal shifts will occur with any tube .. but you will not lose the slam and the power expected out of an SS which the leben brings about along with the micro dynamics and the tube like immediacy & fluidity across the full range....and thats a pretty unique combination (of course which would mean compromises with what an SET lover would expect)