I've used several models of ARC Linestages. Started with LS-1, then LS-3, then LS-2B Mk II. My current linestage is the LS-25 Mk I with GNSC Ref mod. I had the LS-2B Mk II for 8 years prior to the LS-25. The LS-2B is simply not in the same league as the LS-25. The LS-25 has more clarity, more extensions at both ends, and bigger and better defined soundstages.
We had compared mine against a friend's Ref 2 Mk II. It was a coin toss. The Ref 2 was better in certain areas, while the modded LS-25 excelled at other areas. The price of buying a used LS-25 and getting it modded by GNSC was about the same two years ago as buying a used Ref 2 Mk II. The benefit of the LS-25 was that I would be able to roll other NOS tubes to change/improve the sound. During the comparison, I was using a quad of Siemens Falcon 6922s that came with the mod. I personally like Amperex tubes better. I think if I had some Amperex tubes in there, the outcome would have been different, as some of the attributes that we had discussed during the comparison sounded more like characteristics of the Siemens tubes rather than the linestage itself.
FrankC