Can an Audio 20 Radio (with CD Changer) connect to a Harman Kardon amp (with 12 speakers)?

[RJV1]

I have a highly optioned '16 A250 4Matic which I am parting out. It has the Harman Kardon Logic 7 sound system (Code 810) using Comand APS NTG5/NTG5.5, so has the HK amp and sub in the trunk and 11 HK speakers elsewhere. I have dismantled the entire car (down to the bare body shell) and so I have all the audio system components - head unit, 8 inch display, sub/amp, DAB receiver, 11 other speakers, C pillar trim panels (for surround speakers), several antenna, rear view camera, and the entire and fully intact wiring harness (including the MOST fibre optics).

I've done this with a view to installing the HK system (or if too difficult, the DAB receiver) in one of my other A250s which are :

- a 2014 A250 Sports with Audio 20 Radio with CD Changer (Code 510), and
- a 2015 A250 Sports with Radio Audio 20 (Code 523)

I'm aware that one of the big challenges is these units drive their 6 speakers via copper wires directly from the head unit, whereas the Comand unit sends line level signal via the optic fibre to the trunk mounted HK amp which then sends amplified audio via copper wires to the 12 speakers (so in the opposite direction). So a lot of re-wiring to be done but that's well within my abilities.

In researching this I'm getting spooked by suggestions that I have to swap steering wheels, possibly the front SAM, unlock and recode the Comand unit (because its changing vehicles) and that there might also be conflicts with the instrument cluster, the engine ECU and the ignition lock. There was even a suggestion that something in the transmission electronics would be in conflict with the new head unit. Also, as the Comand came from a 4Matic vehicle there's likely to be menus that don't work (engine instrumentation, active suspension, ambient lighting etc.). I gather that the DAB receiver uses 2 antennae - one in the windscreen and the other in the rear hatch window, and the two cars with Audio 20 won't have this rear hatch window antenna. This mountain may be too high to climb.

So I am wondering if there are less ambitious/less challenging options open to me to make use of the HK amp/sub and 12 HK speakers and/or just the DAB receiver?

1. I think the Audio 20 Radio with CD Changer (Code 510) - which is part number A2469010902 - has an unused MOST fibre optic connection on the rear panel. If I disconnect the 4 pairs of copper speaker wires currently there in my 2014 car and run a new MOST fibre optic cable from this head unit to the HK amp (and return loop) and run 12 pairs of copper speaker wires from the HK amp to the 12 HK speakers will this set up work? Will the Audio 20 head unit auto detect the change or do I need to configure the head unit to tell it the HK amp is now installed.
2. Separately, if I install the DAB receiver in the same new Most fibre optic loop will the Audio 20 Radio with CD Changer (Code 510) be able to receive and play digital radio (will it suddenly appear as an option in one of the menus?) I'm not keen to replace the rear hatch window glass to overcome the absence of a second antenna - is there an aftermarket antenna solution for this (note that the DAB receiver installs behind the right side panel in the trunk).
3. I would like to do options (1) and (2) if viable, but if (1) is not then is option (2) still viable?

I gather that none of the above 3 options are viable with my second car - Radio Audio 20 (Code 523) - which is part A2469011605 - because apparently there is no MOST optic fibre connection but I'm not sure of this. I would be grateful for any advice on this.

I'm sure some of you will say don't bother with any of this and just buy an aftermarket system. But I have a full HK system in my garage, plenty of spare time and I enjoy a technical challenge - provided there is at least an 80% chance of success and a pathway back if it fails ! I'll have a few parts left over (Comand head unit, 8 inch display, media hub, 6 standard speakers etc.) but that's OK. I also have access to the MB EPC/WIS system so can get all the relevant wiring diagrams.

I'll attach a few photos of the 2016 model body wiring harness and some of the audio system components - I just laid it out roughly to remind myself how it all fits together.

Thanks in advance for all help/advice.