Hi Cdc...
Any album had to be remastered before it was put on CD, because it had to be transferred from analog to digital (at least once). There's no way that album was digitally remastered in 1976. Both versions could have used the original master tapes...that has nothing to do with digital remastering. I think the question is, were both versions pressed from the same digital masters? Based on your description, it sounds like one of them was probably the original digital master for the original CD release (from the mid-late 80s) and the other was a newer (or different) digital remaster from 1990.
Remastering isn't always a good thing...it depends on how well the first one was done, how well the second was done, the equipment used in both cases, etc. The 1990 version was probably a remaster done by the label. BMG may have produced the copies and released them, but they probably had nothing to do with the remastering. Companies like BMG usually get a license to produce copies with their names on them, but they get the masters from the labels...they don't make them themselves.
And yes...I do think you're hearing the differences you described. Almost all CDs are mastered "louder" these days, which usually means more compression. Mainstream pop/rock is usally the worst, but almost all recordings are probably compressed to some extent in the mastering process...even if it's very little. The amount it affects the recording and dynamics depends on the talent of the person doing the mastering. The digital mastering equipment has improved technically and a new remaster *should* sound better than an old 80s master, but there are many that are compressed WAY too much. Excess compression squashes the loudest signals and raises the volume on the quiter signals, so it will bring up the volume level of the background details (more breath on vocals, more decay on instruments, more background or room noise, etc), but dynamics suffer. That's why so many CDs become fatiguing. It sounds like that very of 2112 suffers from bad mastering, but it probably doesn't have anything to do with BMG.