In other news, I started working on reverse engineering the *.RS file format today. This is the music sequence files that PAGE R uses. Even without debugging directly on the machine, I can already see several patterns going on in the binary data.
First off, the file is split up into 0x80-byte sized chunks. The header has some magic bytes (0x0102) in the beginning and then the speed value of the song. The speed value is different from tempo (since we're dealing with PIT timers and stuff instead of a MIDI clock) so in order to figure out the speed value of your song, you need to divide 314160 by the song's BPM. So, if your song's BPM is 120, then the speed value will be 2618 (314160/120 = 2618).
I'm not 100% sure, but I'm pretty confident the next two bytes are the time signature of the song. The two values I've seen so far are 0x0404 and 0x0804, both of which are valid time signature that are used by the sequencer (4/4 and 8/4).
The last thing that I found out is that the chunk at offset 0x680 is either always full of 0xE5 bytes or zeroed out. I don't know why that's the case.
I'll post more updates on the format as soon as I discover them!