I've noticed more distortion too, I thought it was simply more digital clipping possibly introduced by the new impedence settings (the sound reminds me of the X3 :/ ) and would just need tweaking of those values, but so far that doesn't seem to have any effect (using very low output active pups to test with).  I'm also undecided as to whether I should simply roll back the update, I need to do some a/b comparisons though with both to see if it's real or whether it's just some psychoaccoustic effect.

I just downloaded the HD500 Advanced Guide: Rev. B, v1.40.  I haven't perused it, but did see that it includes the hard gate.

I'm still working on it.. my go to j800-tread patch sounds like crap now. No input clipping.. seem like more noticeble trailing distortion. I need to spend more time with edit on existing patches maybe.

Same here. I have tried both "Yes" and "No" several times; no new presets either way.

Also, the HD500 advanced guide is now revision B while the previous was F.. ..the HD Pro manual seems to be an updated version, though.

EDIT: Should read before write; apparently this is one of the Known issues mentioned in the release notes; The new presets are there, but the set list names are unchanged. Weird, that L6 was not able to change the set list names!!

Ref.:

• Set List Names – If during the update process new presets are optionally loaded to over-write the previous set, Set List names may not correlate to the new presets appropriately.  This is because renaming Set Lists is not a part of the firmware update process.  Set List names may be changed in the hardware using a variety of methods: 
• Manual - Set Lists may be renamed manually by simply highlighting a Set List name and pressing the Save button.  Use the four encoders beneath the main display and press Save to complete.
  
  The presets in firmware v1.4.0 correlate to the following Set List names, as seen in the main display from left to right, top to bottom:
  
  BEST OF HD
  FX HEAVY
  SONGS / STYLE
  BASS/ACO/VOC
  L6LINK <-> DT
  USER 1
  USER 2
  USER 3

You're right - looks like the Editor hasn't caught up with the firmware just yet. I would expect it very soon, but I don't know for sure.

Yes, I tend to use nearly totally dry patches anyway, just the amp.  Though it was more pronounced with my older patches where there were effects too.  Not sure what's changed, but it's almost like the signal is being compressed somehow, it's very dead and non-reactive, hard to clean up with different pick attack/volume on the guitar now, it's like the whole unit has changed.  Master no longer seems to mix back to the Pre sound either, but it acts more like a real world amp master volume actually bringing volume down to 0 rather than blending, not sure what to make of that.  Maybe it's how it should have been all along, but it seems like it's a change.

Dunno, I'll have to play some more, it's odd as I'm pretty sure L6 would have mentioned if any of that stuff had actually been changed/adjusted because it would result in pretty major changes to patches and sounds.  I really do need to go back and revert then try out some things see if it was different or if i'm just imagining things.

Input Z was my first guess too, and I'll continue to play but so far changing it doesn't seem to make much of a difference for me at any setting.  It's odd as based on the release notes that's the *only* thing that's meant to have changed for my and new tones (I already set them up with just single input).

Oh well, I should probably just roll back the firmware and wait for the next update in June.