@gand, have you tried this (TJH’s workaround above)?
„I’ve just set “Soundcard = sysdefault-snd_hifiberry_dacplus…” in Squeezelight advanced settings (it was equal-equal)
My workaround was to give up on the Digi+ and get the Hifiberry Dac Pro instead. RCA outs worked from that right away and everything has been working great ever since. I realize that’s not really a workaround but a capitulation strategy.