jafant, I came from a Ref 5 SE and was able to compare both side by side. The 5 SE is a wonderful preamp and loved it dearly. Comparing the two, I could not go back after listening to the 6.
By comparison the the 6 is faster yet sweeter sounding while adding detail. The bass especially is more defined while sounding fuller at the same time. Soundstage is wider, but probably the biggest change is the depth of soundstage. The great depth the ref 6 offers leads to some stunning layering and very precise imaging all adding up to more holistic you are there feeling.