I had exactly the same problem. I was using 2016 as my client only had 2016, and wasn't a Softplan + subscriber.
Tech supports response was ..
"There is no other automated method. You will need to manually sent the others there supplemental, supporting files. Else, consider creating a reView model (File > reView > Export reView Model File while in a 3D tab). This will create a reView model file (*.svm), along with a corresponding folder that contains the textures for that model. Email the model file and the texture folder (zipped up for convenience), and have them use the desktop reView viewer to look at the 3D model."
However, my client didn't want to view it in the viewer, she wanted to view it correctly in her version of Softplan. I had to put everytthing together and zip it up. Even then we had to do some on the fly, fixing with custom 3D symbols.