As far as the D7 changes go, I rounded out a few of the parts on the boom, modified the launch bay superstructure, modeled the retractable disruptor turrets, modeled in the forward wing insets, altered the torpedo tube and obviously remapped the whole ship down to six textures. As I stated on the DRS forums, my D7 was never meant to be a canon representation and is more of a blending of the TOS, Phase II, and TMP versions. Sort of a transition from TOS to the K'tinga.
Regarding a D6, I'd say that it would be noticeably different. It could incorporate elements from the D5 from Enterprise with early stages of the D7 design, or just have it's own unique style.
I wasn't too familiar with the Akyazi myself and got conflicting references from various sites. There's a number of subclasses, not to mention everyone seems to have their own take on the ship's details. I just took the most common of them and used the rest to fill in any gaps.