Is the top sub-display mandatory to have? will the navi work without it?
The upper sub display and upper dash panel is required. If you don't have that, you will not be able to enter the radio's theft code, or see your clock, or temp displays.
The parts you need are as follows: Upper sub display, upper dash panel, Navi Head Unit, DVD-ROM drive, DVD-ROM drive mounting bracket, GPS antenna, DVD-ROM map disc. You need two custom-made harnesses. One harness connects the head unit and DVD-ROM drive into the vehicle's main audio harness with power. The other harness connects the upper sub display to the Navi head unit. Three additional wires are also spliced into the ECU.
There are two navi models, 2003-2005 and 2006-2007. 2004-2007 are also XM ready models which require a sub display from the 2004 or later model years. 2003 units are not XM ready and must use the upper sub display from the 2003 model year. 2003-2005 use the Orange DVD and 2006 and later use a white DVD. They are not inter-changable. Also, the head units from the sedans and coupes have different button illumination. Sedans have green/white illumination and coupes have red illumination.
You have about half the parts and without the custom-made harnesses, you won't be able to install it. I don't know what Martin charges for the harnesses these days, but it may be in the ballpark of about $500.