Forgot to mention. I also got their Augie drivers. The baffle is going to be made of maple with 2 drivers (1 Silver Iris and 1 Augie) per side.

Darrel and Diane are practically a neighbor of mine (about a 90 minute drive).  He was a member on the former Decware forum where he linked up with HurdyGurdy Dave (who does his crossovers and gave him lots of technical guidance).  We're all from Michigan and so got together before he started Hawthorne Audio where we heard Ziggy's original Torii, his SE34I, and a huge, heavy, complex pair of speakers he'd built.  And I was at a bigger gathering where he introduced the 15 inch Silver Iris.

HurdyGurdy Dave lives closer to me and is pretty much home bound so I visit him occasionally and get chances to hear so many versions (production and otherwise) of the Iris that I get confused.  The Sterlings do provide more resolution and if your going to add an Augie, I'd go with the smaller coax, as the 15 incher has a somewhat noticable "hole" in dispersion between the big woofer and the tweeter.  By themselves the 15 inch coax drivers provide all the bass you need (there is little difference with and without the Augie, even with extremely bass heavy music).

I've also heard the Sterling Iris 15 inchers at the 2008 AKFest and these were only one of three speakers there that were capable of deeper bass that weren't muddy/boomy in these terrible little hotel rooms.  (And Diane makes great little cookies!)

Like any open baffle they need open space behind and present a very large/diffuse soundstage (which frankly causes them to suffer from a lack of ultimate resolution).  Amazingly they don't need a baffle, just a stand will do.  If you can live with speakers on the floor, sit away from them, and give them room behind, you will be treated to speakers that your money is invested almost entirely in drivers versus cabinetry.