Just thought I'd give an update.
I got the HE-400 in the mail and tested them out. First impression was mixed for me as some material didn't seem to shine on these headphones. The most significant was any songs that had cymbals in them. They just sounded strange, like they weren't able to reproduce what a cymbal is supposed to sound like. Almost too harsh, like the effect sibilance has on "s" sounds.
(I'm not saying these headphones have sibilance)
On the other hand, they are very detailed as most other people have pointed out. Jazz recordings sounded especially nice as there was a very nice separation of instruments and level of detail not usually present on other headphones (minus the cymbal issue).
Bass was a concern but it wasn't lacking. Its hard to describe, but because they're an open design, there's a very "airy" and spacious nature to their sound. Its not bad per say, just different than what you may be accustomed to with closed or semi-closed headphones.
Compared to the Superlux, they're head and shoulders above (naturally) and I especially liked the fact that I could crank the volume right up and not have any discomfort. Something I couldn't say about the Superlux.
Thinking I was very confident in liking the NAD VISO HP50 over the HE-400, I went to the store with both headphones to do a quick comparison and walked away with a dilemma that sounds like a recurring theme in our community. I did like the NAD better for comfort and look, but the HE-400 have an amount of detail that's missing on the NAD.
I ended up deciding on the NAD but only because the goal is for me and my wife to use these headphones at the same time (and using different sets would produce different volume levels). While comfort and weight weren't on my list of "needs", the HE-400 do really push the envelope for what's reasonable. They're just on the cusp of being a little too imposing.
tl;dr
If you're in Canada, getting an open-box HE-400 from Razordog Audio is a great deal
(mine was $249+$30 s/h which came to $307 after conversion to CDN).
For the NAD VISO HP50, I found them at Bay Bloor Radio for $280 and also on
Headphone Bar for online.
Thanks again to all the help from the community, much appreciated.