I just noticed (ok, I should have done this before) that I hear swapped output from my Hifiberry DAC+, which is installed on my RPi 3B+. Left channel is played on the right, and vice-versa. Surfing the Internet, I heard that the audio pinout could have been inverted from previous RPi 3B: this could be the issue, as I got the abnormal behavior also with other OSes on my Rpi. With the original analog output jack everything is ok, as expected.
The question is this: is that just an issue of my configuration and, if not, how could I proper fix it, possibly the soft(ware) way. I mean, I wouldn't like to swap cables, because I got the jack 3.5 mm DAC version I spent last two hours with SSH terminal and asound.conf, without any success.
Update: I wrote to Hifiberry, and they quick replied that the PCB of the DAC+ jack version has inverted channels "by design", as it was the only way to make it compact. Shame there's no mention of it anywhere (box, instructions, ...), and no cable was included to swap the channels.
Thanks God my cousin has good electronic skills, so this evening he cut one jack and soldered the wires to a brand new one, inverting the channels.