^ what he said...i just ordered a 6600 because its what im looking for but the 7000 has a superior EQ. And the ability to run the 5.1 is only available on the 7000 and the 5000.
The 6600 looks much more intergrated and factory if you have the right dash for it. I am not a huge fan of flip outs but they both have excellent navi software.
i went through the same thing. i wanted competition sq and good nav. but i wanted a double din. i ended up going with the 7000 and the dcu105. however with both youd be paying a lot. the 6600 has the same sq settings as the 7000 alone plus has 5v preouts. so for sq you would have been best off with the 7000 and dcu, but it would have cost you...as it did me!