External morphs are contained in a pmd file which is read by poser when opening the object.  Opening the object in poser and resaving causes the morphs to be saved with the object.

pz2 files should work, I can't recall any issues I've had.  What is the model or object, perhaps I have it and can check it out.

Klebnor

Lotus 123 ~ S-Render ~ OS/2 WARP ~ IBM 8088 / 4.77 Mhz ~ Hercules Ultima graphics, Hitachi 10 MB HDD, 64K RAM, 12 in diagonal CRT Monitor (16 colors / 60 Hz refresh rate), 240 Watt PS, Dual 1.44 MB Floppies, 2 button mouse input device.  Beige horizontal case.  I don't display my unit.