Yeah, both this release and
GFCA-512~24 are indeed victims of the loudness war. Symphony of the Night does indeed sound louder and more compressed here vs
KICA-7760, whereas the
Selection album on streaming sites sounds about the same as the 1997 album.
From the non-Yamane set, I've only compared Rondo of Blood and Castlevania 64 with their respective 90s releases, and I'm pretty disappointed with both (
Divine Bloodlines,
Beginning,
Slash and
Den in particular all sound much more flatter and squashed). In fact, part of why I bought both boxsets was not only to have "everything" at once, but also because this is the first time Legacy of Darkness got an album release, and yet that also turned out to be a real letdown to me. Missing music, the soundtrack is completely out of chronological order, a bunch of tracks have missing elements/instrumentals, and the overall mastering is even more intrusive than that of CV64's. (On top of the soundtrack being lower quality overall, but I was already aware of that.)
Given that the PS2/DS discs and Castlevania Judgment sound about the same as the original albums, and how
Mournful Serenade sounds just as painful as it did in
LC-1609~10, my guess is that they mastered the older tracks in both sets louder in order to better match the newer albums, whereas the 21st century soundtracks are pure reprints. I have no idea about the
2010 box.
The new Aria of Sorrow recording does sound better than whatever
LC-1453~4 had, but still not all that great to me. (Doesn't help that AoS has the weakest soundtrack out of the GBA trilogy and sounds just boring for the most part.)
At least the
Symphony of the Night MIDI disc was (mostly) spared!