Digital filter Accuphase DF55

Hello,
I'm looking for some information about how the Accuphase DF55 delay works. Here is the use case. The system is an 8 active amps driven by two Accuphase digital filters DF55 (https://www.accuphase.com/cat/df-55_e.pdf). The filter allows to digitally align the delay of all eight drivers based on the farther one which becomes the reference (the 0 point). All other 7 drivers are digitally delayed to align with the reference. This works very well on the filter which has the reference. But on the other filter, which all channels need to aligned with the reference, this doesn't work. The delay alignment is consistent if you set three of the four channels but once you increase the delay of the fourth channel the delay of the three other changes.

More in details, the 8 channels are
First DF55
  • Sub Low initial delay 11.0 m (this becomes the reference, all others need to be aligned on 11.0m)
  • Low initial delay 5.9m, added digital delay +5.1m
  • Low Medium initial delay 6.0m, added digital delay +5m
  • Medium 1 initial delay 6.4m added digital delay +4.6m
Second DF55
  • Medium 2 initial delay 6.9m added digital delay +4.1m
  • High Medium initial delay 5.2m added digital delay +5.2m
  • High initial delay 4.1m added digital delay +6.9m
  • Super High initial delay 3.9m added digital delay +7.1m

When i remeasure the delay once the digital delays have been inserted
First F55
  • Sub low delay 11.0m
  • Low delay 11.0m
  • Low Medium delay 11.0m
  • Medium 1 delay 11.0m
Second DF55
  • Medium 2 delay 4.1m
  • High Medium 5.2m
  • High delay 4.1m
  • Super High 3.9m
Albeit delay was added for Medium 2, High Medium, High, Super High, it has no effect. If the delay of the super high is set to 0, suddenly the delay for Medium 2, High Medium, High and Super High are correct, at 11m. So it seems impossible to correctly align the delay unless one channel as a zero delay value. I would be interested to hear if anyone has crossed this problem and how it could solve it.

Best