AFAICS there's no way to write reference loudness tag as dB. IMO --help output implies that --tagmode=e should write it as dB (and it would be consistent with other written tags):
-s i, --tagmode=i Write ReplayGain 2.0 tags to files.
-s e, --tagmode=e like '-s i', plus extra tags (reference, ranges).
-s l, --tagmode=l like '-s e', but LU units instead of dB.
AFAICS there's no way to write reference loudness tag as dB. IMO
--help
output implies that--tagmode=e
should write it as dB (and it would be consistent with other written tags):loudgain
output:eyeD3
ouput:Runnin on Debian Testing with loudgain 0.6.8 installed from apt: