Which T-rex version are you trying to import?  The basic problem with other Daz characters is the absence of a PCF unless the model is older and has a separate Poser core installer.  Otherwise, your approach to exporting a DAZ model is creating a PCF that can be transferred through DSON, but there is no guarantee that the process will translate into a 100% poseable figure.  You can try following the Genesis 3 & 8 Poser Updater instructions for generating hair and clothing which might generate a Poser-friendly figure.