I too have noticed a much lower output from my phono preamp...
with some recordings playing lower than others...

But...pretty much all my analog sources are a bit lower than than the digital ones...
I also noticed that some older cd's output at unusually low levels...
I'm starting to believe this is a by-product of blending analog and digital...

All this...
without forgetting the human factor...
different sound engineers will yield different sounds...
Still I don't mind....
the records will keep spinnin' !