I just got my Fulla 2 in, and I'm running into the same problem as you two. With my other amplifiers, I've always left the digital levels at 100% and controlled the volume purely in the analog stage. On my Fulla 2, the left channel is noticeably louder than the right anywhere below 9 o'clock, so I'm currently pushing the digital volume all the way down to around 10% to maintain comfortable output levels on my moderately sensitive headphones (HD 558s) while staying in the pot's balanced range. Granted, I generally listen at relatively low volumes, so the built-in gain is also working against me, but I've never run into this problem before.
If you get a chance after your receive the replacements, please report back to let us know whether the channel imbalance is noticeably different. It would be good to know whether it's worth swapping the unit out to try to get one with better channel balance at low levels, or whether the Fulla 2 is just better suited to pairing with less sensitive headphones or listeners that prefer louder volumes.