I have been having exactly the same issue for a long time with my RPi 2 connected to an Arcam irDAC-II. After a few months (and trying all of the above) I have given up and sold my irDAC-II.
In the meantime I have been using the ALLO BOSS dac in that system and this runs fine, but it is no match for the Arcam dac sound wise.
I would really like to get this working again.
Has there been any progress on this issue?