James;
If you have prototypes then I'm guessing you're pretty far along. Please keep in mind, what you are describing are not omnidirectional. They may be polydirectional or perhaps rear-firing, but by doing that you lose many of the advantage of omni's.
I would encourage anyone interested to go to Don Morrison's website and read, preferably all of it. There is fantastic info. there. Then check out Duevel and German Physiks.
I currently run Mirage OMD-28, which I would describe as quasi-omnidirectional. It may appear to be semantics, but there are big differences in launch pattern depending on the omni design. I am aware of various shortcoming of these particular speakers, but despite this, the sound I'm getting is just fantastic. I get to have a realistic concert anytime I want at home. As my kids get older, I plan on upgrading to either Duevel or German Physiks. I grew up playing and being around a lot of non-amplified music, and agree with Morrison and the late Siegfried Linkwitz that un-amplified music is the gold standard.