Are you cutting the neo's flanges to the metal? You will need to do so or comb filtering will start at about 9000hz, and will give you a noticeably flat treble with a distinct loss of "air". Cutting them will give you a line of about 13 or 14 inches, which is going to require the nearfield to be much closer than you might think. You don't want one line in the nearfield and one in the farfield.

Have you read Dr. Jim Griffin's Line Array White Paper?

What are you using for a low end?

Marlboro