Yes its fine to tie all the negatives together I use a grounding bar for this. I have found it helps to bring the negatives from each of the F16v2 outputs. I run all power injection. My second pix shows my fuse box, 4 fed off one power supply and 2 off the other. all negatives off the grounding bar. All negatives off the outputs are back to the ground bar. I'm lucky to be able to keep all of this out of the Rochester winter and dry in the basement. The first 4 outputs are my mega tree, the other 3 are the star and windows, door outlines. the rest are off 4 Differential Receiver Boards. Each are done the same way.
