The files you uploaded indeed looks like an FMOD file (with .fev, .fsb, _bank00 and .wav identifiers).
16 bit PCM: (Big Endian): Music... but it was incredibly fast and high pitched than the normal music in game.
You've probably got the sample rate wrong, what if you try
a lower one?
The thing I notice is that not all of the other snd files behave the same way. Some don't even work with any of the options above. I don't suppose these snd files could actually be encrypted in some way? Upon looking in the Rocket Knight folder, I see two dll files named fmod_event.dll and fmodex.dll. These would be related to the audio, correct?
Nah, it's not encrypted...
FMOD Ex supports the following audio formats: AIFF, ASF, ASX, DLS, FLAC, FSB (FMOD's sample bank format), IT, M3U, MIDI, MOD, MP2, MP3, Ogg Vorbis, PLS, S3M, VAG (PS2/PSP format), WAV, WAX (Windows Media Audio Redirector), WMA, XM, XMA (only on the Xbox 360), as well as raw audio data.
In this case you found a file that contains WAV data, by forcing your soundeditor to specific settings you can get the music out of there. The headers still sound garbled, obviously. The other files may very well be different, for example in MP3 or MOD/IT/XM format. To get all the music out properly, you'll have to run it through a real FMOD engine, either in-game or standalone (if somebody made that). Or you can just download it from the links Rich found, which is a lot less work