Is it possible to be better equipped against them? I realized my crew at the time wasn't really suited for it, but if they have a 100% chance of grabbing anyone and there's around 6 of them at a site, what can you possibly do to combat that? I'm not criticizing, I really like having challenging aliens to deal with, I just don't see how that kind of site could be taken without a few VERY lucky blaster bombs at turn 1.
To me the best way to counter Psi is to screen your troops, develop Psi-Amps and go on the offensive from turn 1, which means disembarking the HWP to spot aliens to mind control them, before the aliens get the chance to do it to you.
In any case, the other day I was rechecking the Psionic equations used and discovered that Psi Strength is also used when calculating the odds for psi attacks (and Psi Skill is also used for defense), which explains why the aliens have been so effective on psi (they have a +50% boost on Redux to help prevent players abusing Psi tactics), and why aliens so many times have 100% chance of control. The boost from Psi Strength is something like 2% increased for each 10 points of Psi Strength, so a Hybrid would have almost 10% additional chance due to the boost (the math might not be totally correct).
I've already revised this for 0.7 by removing the Psi Strength bonus from the psionic aliens, and reducing the Hybrids' Psi Skill. I can modify the 0.5.4 ruleset that you're using if you're finding them too hard. Otherwise, start building Psi Labs everywhere, because you'll really need to boost your soldiers psi stats.
Big day in Reduxland... Happy Cinco de Mayo
Congratulations on your first commander!