I certainly am no expert, I'm still learning this stuff myself.
For the dimmer, relay and switcher packs(Ok, so I just have dimmer packs at the moment), i have been using these clamps. I don't know what company makes them, but I have been getting them at Guitar Center. They are the brushed aluminum as opposed to this other one that is powder-coat black. I stick a clamp into the large hole in the dimmer pack that is at the top and centered, but is on the back side, not on the very top. I then hang it from the upper level of the truss and then screw it down to the truss for safety.
The brushed aluminum clamps are cheaper than the black ones, but seem to be otherwise rated the same. The black ones have a larger screw for mounting to the fixture and it was too large for the holes in the ADJ fixtures.
I would say use clamps to get around the available screws, but make sure the clamps are going to work in your fixture as well.
I know, not perfect, just my novice advice.