Thanks to the assistance of Rob13572468, we confirmed that indeed the GW 500 must be installed immediately ahead of and adjacent to the CD Changer in the fiber optic loop. On his recommendation, I swapped the fiber optic connections between the Voice Control System module and the CD Changer in the trunk. This had the effect of placing the GW 500 directly after the COMAND unit and immediately before the CDC, in the loop (see diagrams without Sirius, below). With that done, then selecting the "iPod" position on the mode selector, and following the procedure to shut down and re-start the MOST bus (turn off COMAND, turn off ignition, remove key, wait approximately 2 minutes, then insert key, turn on ignition, then turn on COMAND), the GW 500 worked!!
Note: In cars with trunk mounted CDCs and also with OE Sirius installation, swap the fiber optic connections between the CDC and the Sirius module in the trunk. See diagrams for MOST with Sirius below.
The MOST bus, unlike the D2B bus, uses a signal in the fiber optic path to "wake up" the equipment on the loop (D2B uses a copper wire for wake-up). The GW 500 is most likely designed to intercept this signal for the CDC, thus keeping the CDC from waking up, and places itself and whatever input is connected to it (iPod, USB device, or AUX) on the loop. When the GW 500 is not immediately adjacent to and prior to the CDC, its ability to keep the CDC "asleep" is intercepted or interfered with by whatever follows the GW 500 on the loop, and the CD Changer wakes up and enters the loop. My best guess, anyway.
I did some photo documentation of the switch of the fiber optics in the trunk. It was not a fun job. I'll try to post it tonight or tomorrow.
Bottom line so far:
The GW 500 works, and the sound quality from the iPod is wonderful (especially since most of the music is stored in high quality formats - not mp3). I do get song title information and elapsed time on the COMAND display (YAY!), but must do more study in the user manual and play with the system a bit more to understand the menu functions better. Only track information and playlist number are displayed on the multifuction (instrument cluster) display. Steering wheel controls work just fine, and in the iPod User Interface mode, all of the iPod functions are available on the iPod (which is why I wanted it in the console, not in the glove compartment; further, the USB input is for music files on thumb drives, and is also the way firmware updates are made, so I wanted it there too). The COMAND CDC controls set normal play, repeat, mix, etc. for the iPod as it does for the CDC.
The lack of adequate documentation is the Achilles' heel of the GW 500. With the unit costing around $500, I feel more like a beta tester, when I should have gotten the gold standard for that cost. However, I expect the results will be worth it, once I learn the interface adequately. The improvement in sound quality over mp3 DVD and the integration with COMAND and steering wheel controls is great.
I hope this documentation and that to follow will help someone. For those who like diagrams, the before-and after MOST fiber optic rings for my '05 W220 are below. Check the phone bulletins on Paul's site for your car - thay are not all configured the same. The change in position of the VCS (Voice Control System) and CDC (CD Changer) in the diagrams is effected by swapping the fiber optic connections between the two. However, I believe that despite the switch, the MOST master controller still sees the CDC as component 4 and the VCS as component 2 on the STAR diagnostics menu, beccause no STAR diagnostics reprogramming is necessary for the installation. I just didn't change it in the diagram.
After the changes, all of the items on the ring - VCS, nav, radio, telephone, etc. worked as before, except that now the GW 500 would replace the CDC in the ring when desired.
I do want to thank Rob13572468 again for his time and patience; we had frequent private message correspondence putting our ideas together to resolve the problem. He is in Chicago, I am in Tampa - but some of his PM traffic is time stamped at 1:30 AM, so I know he worked late to help. His help was invaluable.
