Exporting Displacement map in 16 bit Tiff with Alpha Displacement Exporter plugin
Configure the map to export (Zplug/ MULTI DISPLACEMENT 2/Map Size (Max Map Size slider), Overpaint border thickness (Border slider) and Map quality (DpSubPix slider)).
(For more about installing and using the Displacement Exporter plugin go to ZbrushCentral: http://22.214.171.124/zbc/showthread.php?t=029789.)
Right, configure the Displacement Exporter plugin on the ADE panel (Alpha/DE Option button): PN16 (this is predefinied configuration). Configure this as follows: set the Configuration Status to ON (this way the Red channel will contain the positive, and the Green channel will contain the negative displacement map) and set options: Smooth, Seemless and Vertical Flip to Yes. Export (Export Active Set button or Export Current button).
Saving positive and negative DispMap separately in Photoshop
Save the red and green channel of the exported file as two separate maps into 16 bit Tiff format. Open the exported file in Photoshop, go to the channel palette, select red channel, select all (Crtl + A) then copy it (Ctrl + C). Create a new document (Crtl + N) and paste it (Crtl +V), then go to the layers menu, and select Flatten image. Save the file into 16 bit Tiff format with the name PositiveDispmap (File/Save As). You have to do the same thing with the green channel, but save this one with the name NegativeDispmap.