Just to test this I installed DS3A.  Fired up DS4.6Pro, loaded M4, applied Guy4's texture and adjusted to give skin a bronze metallic look.  Created a new "Mat Testing" folder under Pose in my "DAZ Generation 4" Poser file format library, used File > Save as > Deprecated > Materials Preset to save "Bronze.dsa" preset.  Opened Windows Explorer, navigated to the "Mat Testing" folder, changed the PNG file name from "Bronze.dsa.png" to simply "Bronze.png".  Fired up Notepad, did not type anything just File > Save as to save "Bronze.txt" to "Mat Testing" folder.  Back in Windows Explorer renamed "Bronze.txt" to "Bronze.pz2".  Closed DS4.6Pro, opened DS3A, loaded M4, found preset in Pose/Mat Testing and applied with no errors.