For DPS is the Matrix cube better than the Relics that procs?
It depends on which tier of relic you're referring to. The Matrix cube is roughly on par with a Columi PvE relic or Battlemaster PvP relic so it's a wash as to which you should want to use. For anything higher than that, you want to get rid of the Matrix Cube.
And because I am assault should i get the elemental relic proc
or the internal which ignore armors.
Both elemental and internal ignore K/E damage reduction so that's not really a factor. As far as the game is concerned, they're functionally the same thing.
*However*, there is a difference between the internal proc relics and the elemental proc relics: the elemental proc relics use your Force crit chance and the internal proc relics use your Tech crit chance. As such, since you're a Tech class, you should be using the Internal proc relic since it's going to use your full crit chance (the one listed on your character sheet under the "Tech" tab) rather than just a part of it (as a Tech user, your Force crit chance gains no benefit from your Aim and, as such, is generally ~10% or more lower than your listed Tech chance).
It's not a *major* factor since it amounts to all of ~6 DPS at the absolute top tier, so it's not as if you should go out and get an Internal proc relic to replace your Elemental proc relic if you got an Elemental proc relic already, but, since they cost the same and there is no difference from anything but a damage standpoint, you're better off buying and using the relic appropriate for your power source if you're coming from scratch.