Because the Advent will not be playable/released/known until the full release of Sins, it is very hard to say. I don't think it will be like you are thinking. I am thinking more of the abilities they have being used in various ways on the ships ... like weapon enhancement, shield reinforcement, and or enhanced (or just different) radar.
From the Lore page:
Shocking acts of deviancy, at every level of society, violated the venerable taboos common to all the Trader Worlds. Sinful cerebral integration technologies, unrestricted biological experimentation, strange forms of collectivism, and the wholesale usage of countless neurochemicals were but a few of the transgressions.
From the first GameSpy Preview (12/8/2006)
Eventually, the inhabitants of the worlds that comprise the Trade Order began to encounter some of the more disturbing facets of humanity's interstellar fragmentation -- a "race" calling itself the Advent. Think Star Trek's Borg: they've integrated technology into their physiology, and as a result, bear little resemblance to humanity as we know it.
From the latest GameSpy Preview (9/12/2007):
The Advent are the descendents of humans who were exiled from Trader space ages ago and have returned with bizarre psionic powers.
I would emphasize that the only real known facts are these, and they are vague at best. The keys I see are biological integration of neural augmentations, possible collective intellect, and possible psionic abilities. I would extrapolate that these psionic things would be much like some of the existing upgrades for ships that the TEC has. For instance you might train your crew to mentally disrupt the crew of another ship ... but obviously that would be tiring and strategically focused.
I doubt they'll be going so far as to make there be spell-casting in outer space.
