DVD Navigation System Retrofit with On Board Monitor

I'm retrofitting my auto with a Navigation System in accordance with the BMW DVD Navigation System Retrofit Instructions. Here's what I have:

Year. 2005
Model. 325i
VIN. KW20556
Production Date. 10/04
ETK Screen Printed. 01/22/10
Retrofit Kit No. 65 90 0 391 113
Vehicle Information Printed 1/21/10

The first three images below are of the Navigation Retrofit Installation Instruction pages 1 (Cover) and 4-5 (Parts Listing). The fourth is the Vehicle Information printout with the applicable options for the install highlighted. And the fifth image is of the dealership ETK printout with part numbers of major components highlighted. Those being the (C) Radio (D) Navigation Computer and (E) On-Board Monitor. The letters correspond to the parts listing in the Install Instructions. I've been able to part number and price listings A-S with exception*:

(C) Radio (Professional) 65 12 6 976 963 $638.93 Euro Fitment
(D) Navigation Computer 65 90 9 176 685 $3,154.59 Euro/US Fitment E83
(E) On-Board Monitor 65 52 6 934 411 $1,955.10 USA Fitment

*Yes I know the part number and prices are there, but I do not know if they are the right ones, or the ones that would work here in the U.S.

I've read every post dealing with retrofit and they/you all have been extremely helpful to this point, all 50+. Thank you. Special thanks to Technic and sna77. Like I said, the rest of the install seems simple, but for this I'm at a loss. I was told that for C, D, and E that the part numbers listed were the only ones that would work. I would like to know if I have to buy these exact part numbers or is this just the dealership just trying to make their money? How does fitment with these parts work (i.e. Suppose I have C, D, and E for the E46 platform, but the part numbers are different/old/superseded.) Can they be put together and work? Are there alternate U.S. parts that would cross-reference, that would work as the European parts called for? In the case of (D) Navigation Computer I searched through RealOEM.com and the part number called for an E83 chassis? Weird. And of course, I'd like to save money by sourcing the more expensive out to other vendors (i.e. Aftermarket/E-Bay), but there are so many part numbers out there on these items. The monitor, radio, and computer total at $5,748.62 alone. Most of these listings seem legitimate, (i.e. Buy from our company this C, D, and E will work for an E46 platform) but even if I buy them and they would work flawlessly, oooops, it's the wrong part number and is not compatible with the rest of the system. So far I've sourced 16 out of 19 components successfully but need to get a better idea before I complete these last and most crucial 3. Thank you for your input.