Well, I don't know about how the data is interleaved, but I do know that the utility iso2raw has a command line option "/SCRAMBLE" which, according to itself, scrambles sectors. I wonder if this is the interleaving that is talked about?
Oh, and as an aside, I was reading the pdfs again last night and it turns out that there is a midi interface on the Saturn, but the type of connection isn't midi compliant. That is, while the pins match up, the physical connection isn't the same. Kind of makes me wonder, just how did someone compose music on the Saturn? Not much is really known about the sound chip.