There was a thing called 32-bit cleanliness,
Apple and other programmers sloppily and cleverly used the top 8 bits of the 32-bit bus for their own evil purposes, since Macintosh System 6 used only the first 24 bits of the address bus, This was non-problematic until the first 32-bit Mac System Software, 7.0.0.
Suddenly all code needed to use those bits for addressing. If some programmers had put this sloppy clever code into a ROM, say for example, the ROM in a SE/30, IIcx, and MacIIx, the hardware would need a ROM patch to use the full 32-bit bus on that hardware. The brilliant folks at Connectix came out with a patch called Mode32, which was payware until Apple released their own patch a year or two later. Mode32 became free, which is good, since it was more stable than the Apple 32-bit enabler. Without a patch, the SE/30 hardware could address only 8 MB RAM.
Some adventurous hackers like me also or instead replaced their removable bad SE/30 ROM SIMMs with the removable good ROMs SIMM from a IIsi, IIci, or IIfx. which were scarcer than virgins after a Bacchanal even before Apple clamped down on them and soldered all ROMs to the motherboard evermore.
Since AUX didn't use the SE/30 toolbox ROM, it was never affected by the 32-bit dirty issue.