Dynamic audio playback while playing the game (Vote :D)

Hmm, I know what you mean and in some games (Like Fire Emblem) it works well since the games transition between an overworld and a "Battle Area" but Caslevania games don't really have that. To me its more about setting a mood or ambiance that gets you into a groove as you move through an area. It worked (how well is up to you) in Mirror of Fate because enemy encounters were a bigger focus: enemies had a lot more health and were in general more dangerous than the average 'Vania mob, thus swapping from an "ambient" theme to a "combat" theme made more sense. 

If done poorly the music could bounce back and forth like a hyper child on sugar as you move through a zone OHKO-ing everything.

Yeah right, I mean too much dynamic is just awful chaos, but the most effective psychological theory behind dynamic audio, from what I have read, isn't just one note repetition. In basic music theory the sound of transitioning from A to G# sounds completely different transitioning from G# to A. The notes are the exact same but the context of the notes leaves the listener to hear a higher change in pitch to a lower change in pitch during the transition, so its the in-between part of the notes that you are actually perceiving, Guthrie Govan, a guitar virtuoso states he could hit the same note 5 times in a row and make it sound different each time. If that is true, the purpose of the note's use is what determines the outcome of the final sound and is what makes a composer so important.  Its carefully placed, hard to notice skillful transitions or tonal themes that are shifted accordingly to a situation at hand. The most immediate one that comes to mind is the piano sound in Mass Effect 3, it is present in every single song on the album but in such select areas only the subconscious of a player would pick it up. The composers intended for the piano hook to stick to the player's mind throughout until that final scene where they cut all sound and only had that piano part playing finally. That OST is absolutely brilliant with its dynamic audio; it picks non-invasive, psychological hooks. . This really would be outside an Igavania's norm, though, going full on feels would be really weird, but I think this is still on the level of an indie game, and at least in story mode, indie games tend towards atmosphere and feels. I mean I already hear a thematic similarity between The Galleon of Minerva and The (Currently) Unknown Track. Also I noticed the rain in the demo shifts out as you go through the level, that was awesome!