I have considered several different drivers for the DNA horn which can be found in the design notes for the DNA horn.
http://www.decware.com/newsite/paper120.htmlYou may use this as a guide when you consider drivers for the DNA horn.
I did try a less expensive Tang Band driver, the W5-1611SAF 5" Full Range Speaker with the world's worst results. Please don't waste your time with this one.
I also tried my small Lowther DX55 drivers and they sounded good, but are a primarily a midrange driver so there isn't any real bass weight. I will say, that the DNA horn made that driver, as well as the 4 inch foster drivers used in other horns, have more bass than they did in any other cabinet, but considering what this cabinet is capable of it would be a waste of a good design.
To that effect, I have found a driver that I like 95% as good as the TangBand IF you're going with lower powered amplifiers. In fact the bass was actually better, more correct, less colored. The highs are rolled off, but I still enjoyed it for an evening by itself without adding a tweeter, which it will obviously need. But I think that is fine. A tweeter floating on top of the cabinet would be very nice.
The driver is an AuraSound buy out at Madisound, so who knows how many they have or how long. The price is right a 3.60 ea.
http://www.madisoundspeakerstore.com/approx-5-fullrange/aurasound-ns525-255-8a-5... 
Again, this is the best sounding driver I've heard compared to the original, and the bass extension is the same.
-Steve