Sorry, but the first post is incorrect.
Second poster is correct, along with the Disk II controller update.
P5 and P6 are the ROMS that were replaced, but otherwise no difference. One is a state machine, the other contained the boot code.
The Apple /// did not use DOS 3.2 or 3.3, and emulation mode was NOT built into the ///, but was initiated by booting the emulation disk.
What WAS done for the on the Apple II series due to the A3 was ProDOS.
ProDOS IS SOS. The only actual difference is the calling method. ProDOS used a JSR $BF00 followed by a command byte and a pointer to a parameter list. SOS used a BRK instead of the JSR, otherwise they were identical, even to the command byte and parameter lists.
DOS 3.2 and 3.3 use 256 byte sectors. SOS, ProDOS and other OSs such as Pascal use 2 sectors (and yes, they are still sectors) per block for 512 bytes. The sector interleave is different as well to optimize for 2 sectors at a time instead of one. In disk images, the file extension is supposed to indicate which one. .po for ProDOS order, .do for DOS order. There are others, but the actual disk data portion is still one or the other, with possibly a header (.2mg) or a generic .dsk.
Emulation mode was not limited by the disk format (3.2 or 3.3 or ProDOS), but the real limit was due to there being only 48K of memory available to the OS in emulation mode. ProDOS requires 64K, and therefore cannot be used in emulation mode.
DOS 3.3 was released well before the A3 came out. I've been using the A2 since before disk drives were available, and was working in a computer store during the time of the drives becoming available and the release of the A3.
BTW, we did NOT use Apple's drop 3 inches method of "fixing" the A3. We removed the cover and pressed all the chips into place by hand before even powering it on to check it.