Hi Matt, regarding the "draw", do you mean draw more than N amps?
Yes the Triac (solid state) can control something up to 5A, while the relays can support 10A.
Notice that in general, and unless it is above 5A, you want your high powered equipment to be on the Triac's, as mechanical relays can fuse in the long run when used to control something drawing a lot of electricity.
While the Triacs should actually not be used to control something that is not pulling enough energy, for instance a dosing pump, which could be left "on" by a Triac.
It is counter-intuitive I know...
In your case, I would mostly be concerned about the total draw for a single EB8. I would plug a single metal halide to the EB8 and check what is the draw like that. Remember the limit is 15A *total*. If you are running a 400W metal halide, I would expect the draw to be in the 3.5 -> 4A range.