Did you see the tutorial below? There’s a way to do it manually that does not split the dots like the image splitter does…you might get a better result with that kind of image.
As far as it being too complex, you might have been able to process the whole thing by simply lowering the LPI a little. Anything over 195 LPI is going to get you complete coverage with the engraving, and lowering that will sometimes let the entire file process as a whole. You should be able to get up to full bed size processing on 195 LPI. (The default for SD is 270. Or it used to be.)
Tutorial for splitting an image:
Like everyone above suggested, I wouldn’t try to combine them in the GFUI yet. It will be better in some sort of outside design software.