There is much larger register file with the IW. The LMC configuration register (52h) should tell you the DRAM and ROM configuration of the IW in a few of its bits.

I'm trying to figure out if I need a mode where it totally blacks-out the IW specific registers and bits or if the IW is truely a pure super-set of the GF1; eg will the older SB/MIDI emulation utilities run on the IW unchanged.