Thank you for all the helpful posts here. In the end I decided to buy a pair of Pass XA 100.5 new instead of going with a used Lamm M1.2 (here in Italy the importer asks for a prohibitive price of 29.000 so buying a new pair wasn't really an option). Yesterday I picked up the Pass and plugged them into DCS. I cannot comment on the sound with or without pre as I traded my ARC Referernce 3 for the Pass. I'm already completely happy with the sound (compared to the old setup with ARC Ref3 and Parasound Halo JC1) noticing a big improvement in terms of musical fluidity, texture, coherence and bottom weight (although the Parasound had a more defined, punchy bass). I'm using the 2V output of the DCS and did not recognize any loss of detail at lower listening levels (normally the volume of the DCS is at -25db to -30 db).
However, I'll give it a try with a goob pre like the ARC Ref 5 or the Pass XP 20.
However, I'll give it a try with a goob pre like the ARC Ref 5 or the Pass XP 20.