For me i found early on in owning Lyr 3 that gain setting makes no difference to me so have been using high gain since then (planars), never tried low gain with the 1578.
Something else i find weird though but could be my imagination, sometimes when volume pot is lower than i would like for headphones i turn up volume on PC (software) and sometimes seems to make it sound better, only happens because i'm too lazy to get off couch to change proper volume pot

So Lyr 3 could be sensitive to input level or could be my imagination.