If anyone is interested. I got my HD-800 today and have been listening for a bit now and really like it. The Concero certainly does the HD-800 justice, especially with the IIR filter engaged. The filter differences are slightly more noticeable with the HD-800 than my other headphones. Of course, this is through my amp, and personal tastes, so YMMV. I'm sure there is greater performance that can be had with the HD-800 but the Concero is certainly not a noticeably weak link and I have no particular itch to upgrade right now.
And also, I am using a slight bit of EQ to tame the sibilance with the HD-800 but no more than 2db and within JRiver the DSP is done in 64bit floating point so it shouldn't affect the fidelity much if any at all, at least not that I can tell.