When you saved your obj file to the thumb drive: Did you save its .mtl and image file (.png or .jpg) along with it? All three files have to be in the very same directory.
Don't use some external way like "open with" from Finder/Explorer to open textured files. Instead use Import from within Meshmixer.
What's about the GPU on you MacPro?
What does the log (menu:Help/ShowApplicationLog) say about texture shaders?
Scroll down to [System Information] and the following lines...
(Be aware that there will be OpenGL errors on OSX due to its 2.1 limitation im compatibility mode but TEXTURED, TEXTURED_UNLIT, and TEXTURED_TILED should compile)