Is the imbalance new? Were the Amiron Home headphones level balanced ok from the start?, and have now developed this imbalance over time?Headphones are not new, they do the same with different sources.
It is possible the jack / internal wiring is "bad" and needs fixing as it is a "drop" in volume.
Even if not new you might be able to use your warranty to get them repaired.
I updated my last post, please refresh and check for options to adjust the output.