Hi Ronnie,
I'll have to go with my original gut feel which was that I didn't like it. As you know the SQ of the ID40/v6 is really quite excellent (would go as far as saying awesome), so, when I felt over a few days that all was not quite as good as it should be I started to worry.
I had no idea that replay gain was on so all my listening was done by playing at whatever volume I felt like (to my ear not the volume scale). But, it was like the shine had been rubbed off all the nice highs and "tings" of the treble, hi-hats etc. I even thought that 3D placement/imaging was lost to an extent also.
With it (Xfade) switched off it all came back in spades (because levelling then switched off)
I can only think that I'd set replay gain as a test and forgotten about it as I probably didn't hear it do anything.
When I then wondered how x-fade worked and it is when gain was affected. I didn't initially link the two as they were a couple weeks apart.
FWIW - Xfade would work much better if M implemented it only to work with songs from different albums. That way it would not destroy the gapless albums e.g. DSOTM and any DJ mix type albums.