I don't think your photo of the HK amplifier is correct. It seems to show the ASD module, not the amp. See the second photo on this page for the connections on the HK amplifier:
https://alpincars.com/en/amplifiers/...8-2622876.html The connector in the upper right corner is the MOST interface (see here:
https://www.newtis.info/tisv2/a/en/g...ier/1VnYgsuKRh)
Your amplifier should look like this:
https://www.newtis.info/tisv2/a/en/g...ier/1VnYqbFtrQ There is no MOST interface, so there likely is no MOST cable going from the head unit to the area of the amplifier in your car. But check it. If it's there, then things will be a lot simpler.