Youve got to remember that a lot of the vids for displacements for Zbrush are either for version 1 and/or 2 not for 3.

Its quite hard to get to grips with but well worth it, the "old" method was just to export displacements form Z (probably the way your doing) then adjust them in PS , then the displacement mapper came out which makes the process a lot easier.

Also youve got to remember that maya was different back then and maybe didnt support 16 bit tiff's (not too sure as it was before my time with 3d)

The process I use is model in Z3 then export to Z2 then reconstruct the sub divs, export the low poly object, re-uv in maya import as a morph target for the low level model, use the multidisplacement mapper at 2048, 32 bit tif, then convert to a .map (if I feel like it) then make up the shading network using the std route (approximation editor etc etc)