Jim,
I've heard open baffles that Darrel built using similarly sized coaxial driver before he went commercial with the Silver Iris drivers. They developed as much bass as I suppose you can expect from open baffles, were efficient (we were running 2 wpc in a 4,000 cu. ft. room), and offered incredibly flexible positioning options (for yucks he even tried them laying down on the floor firing straight up). Frankly open baffle is so simple, like Darrel states, that its really just a matter of finding the right drivers. So why pay more?
Although I've met Eddie Vaughn and exchanged a few posts, I've never heard one of his creations, but search the Decware Forum for his sage advice and the magic he has performed on other amps.
Darrel lives about a two hour drive away. Visiting him is definitely on my wish list.
BTW, hope I haven't offended anyone by posting this (here?).