[simonchs]

f20 hk amp is not part of most ring

After a bit more googling, I can see that the HK system is not part of the MOST ring, you're right! 

I've read reports of successful external amp retrofits that do become part of MOST, but I think that's for another day...

Thanks!

It is because BMW made a "higher" audio level then high audio system 
For F2x vehicle, H/K amp is 360W without MOST
For F3x vehicle, H/K amp is 600W with MOST

These 2 amp can be crossover by proper wiring and FDL coding; my F20 had retrofitted H/K amp 600W with MOST.

Did you need to re-pin the non MOST HK amp to work on the MOST HK amp or are the connections the same?

obviously the amp needs to be added to the optical loop.

The pin assignment and connector are totally different between non MOST H/K amp and MOST H/K amp; I’ve custom made a new harness, amp <-> speakers with those hifi “Gold x Silver” cable; and the 600W MOST H/K amp got standalone 2-pin power port, I’ve connected to battery terminals; also MOST fibre, dropped the amp into existing MOST ring.