I can only joy while reading these posts. The music of the Aquaria is really something to wonder about. When i first started to play, the beautiful music in the menu was enough to convince me that this game was totally worth of its price. Generally, music in Aquaria succeeds to create the atmosphere of the underwater world; it is relaxing, mysterious and simply
touching. I can hardly imagine any fitting music for this game.
Congratulations to the makers!

Soundtrack would be the obvious choice for me, or mp3 -files. With some extra-music (piano!), like You suggested, it would be a success. There are many nice melodies in Aquaria, and i usually travel from place to place just to listen those (in game, of course).
However, i have noticed that
listening too much the music you like will spoil (or harm) the actual game-experience. The music unique to some place, or event, won´t feel exotic anymore; you just get fed up with it. That´s my problem, because i can´t just stop listening good music ( The Jukebox-mod is too much for me).

I hope i won´t ruin my Aquaria-experience. Maybe i should complete the game first...
I had to say something, though you guys have mostly said eveything needed.
(And i should practice to write more in English too...geez, haven´t done this for years...)