Norichika Sato is listed in lots of other places as well, as in sound effects. So I'm guessing Ishiwatari is the one that actually composes the music. As in making the note-charts, the tabs and a midi for showing/listening purposes (which we've heard on Buluraji a few times), while Sato is the one that makes the transfer to the recording band, on top of arranging the recordings with extra SFX and what not until we have the finished product.
So in short, Daisuke composes the music, while Sato is the Sound-Dude that makes it all come to life. That's my guess at least.
What Shunsuke Takizawa does, however I have no idea. I couldn't find him anywhere else on the sound-part of the credits.