Bizhawk-Vanguard exposes the following domains in RTC:
RDRAM (Rewindable) : This is the console's main RAM. It will be either 4mb or 8mb depending if the emulating N64 is using an Expansion Pack or not.
ROM : This is the game's rom as perceived by the emulator.
MI Interface : The registers for the CPU itself. Probably avoid this
PI Register : Peripheral interface registers. Controllers and stuff
SI Register : Serial Interface registers. Registers for use by anything that uses the N64's serial port
VI Register : The registers for the video interface. Contains data related to drawing the current frame. Not really gonna get anything out of this besides maybe enabling some filters (such as anti-ailiasing)
RI Register :
AI Register : The registers for the sound chip. Doesn't actually contain the data for the music, just points to where the music is in rdram for the hardware
System Bus :