If anyone's using cans that Sonarworks doesn't support here are a couple other things I find useful...
This is a crossfeed plugin (kind of like a less featured SPL Phonitor.) It brings the stereo image in (60º is my fav) and helps to create the impression of a center image... You can also adjust the level of the center image and fold down to mono. (Can be used with Reference/Systemwide.)
Spatial Soundcard Pro
This is my go to headphone utility now.
Spatial Sound Card lets you headphone monitor through binaurally recorded speaker/room impulses sampled from a bunch of control rooms, post production facilities, (and there's a mastering room as well.) It's the only headphone solution I've found where kick drum 'knock' translates in cans, which it does it really well... Soundstaging is pretty amazing as well. The binaural impulses reproduce surround sound in headphones, which is pretty increible. (Mike Thornton's review below shows how effective it is at reproducing 5.1 in cans. A few video games have adapted this into their sound platform....)
It also has corrective EQ for a few headphone models, (not many models but imagine there's a way you to use it in tandem with Reference 3. Prolly not systemwide though since SSC is its own virtual audio device...)
For unsupported headphone models I made my own corrective EQ using the HD600 preset and headphone graphs from this site: HeadRoom Headphone graphs
It takes a little bit to get used to but can't imagine working without it now. The low end in particular translates really well and sounds like the low end you hear in a really good room.
PT Expert Spatial Sound Card 5.1 demo