I have noted that similar SIMMs have identical (100% the same) main ROMs and that only the presets are different. So that SIMM 12 and SIMM 22 (both "sounds of the ZR" but the second one was from the Halo whereas the first was stand alone - buy in a box) have competely matching main ROMs.�
Most SIMMs barely use half of 2MB of preset memory with some using less than 1MB (even well under 1MB). Since the P2K modules copy the contents of preset to RAM on start up (and don't access it later) the limitation in expanding preset memory is the amount of DRAM that you have. There are no SIMMs with more than 2MB of preset except the 32MB FLASH SIMM which has 4MB of preset FLASH though I've no idea if you can really use that much.�
The command stations have a fixed 8MB SDRAM chip whereas the P2K modules came with a 4MB or 8MB DRAM SIMM although they will accept and use a 16MB DRAM SIMM. So if we max out the preset memory with additional stuff (more arps, more presets, more demos etc) then it may end up becoming not useable. That's because if you have too many SIMMs in your module (beyond the ability of the module to store the preset information in DRAM the presets from the last SIMM(s) are not read at all and you can't see anything from them. I guess that the P2K OS checks the size of the preset ROM and gives up if the space is too large.
As I have previously observed the main memory is made of stock standard .E4B files. From the structure it looks possible to have up to 4 .E4B files in one SIMM. I don't think that the preset memory cares whether they're .E4B files or not since it just points to names and wave files within the main SIMM rather than the .E4B specific stuff. I did note that the XL1/XL7/XK6 main memories are all identical. but they each contain two 16MB images - the Audity 2000 v10 E4B, and the EROM 2 V1.2B which are the 16MB ROM images used in the AUDITY 2K.
If there's no one helping me, it will be a long time before I can get to the stage of putting our own presets and waves into a SIMM. But I will try and copy existing SIMMs in the next week or two.�