emusonacid!

Hi. Not having much luck with the search engine today.

My guess is that "z-plane synthesis" only refers to filtering, and that the Morpheus is essentially a ROMpler. Or is there more to the Morpheus?

The main difference between the E4 and the Morpheus are the number of filters.
Morpheus has 197 different filter-types which have between 2 and 14 poles.
The E4-series has just 21 filter-types.
Morpheus was the first in a row of Z-Plane Filter Synthesizers from E-mu and you could not modify the set of samples as the Morpheus is, as you already mentioned, a ROMpler.

The successors like Xtreme Lead XL-1, Command Station XL-7, MP7 & PX-7 have 50 filter-types.
Actually the Emulator X3 software-sampler has 55 filter-types where you also have the possibility to design your own filter.

Thanks for the detailed response! Wish they made the Emulator X for Mac...

Edit: Bogus question: Answered!