two interesting builds I though up

[John Campbell]

I believe he is referring to the -4 penalty you take for firing the crossbow one-handed, not the TWF penalty.

Which stacks with the TWF penalties, so even if you've got Two-Weapon Fighting and Oversized Two-Weapon Fighting, you're at -6/-6 trying to shoot dual heavy crossbows like you're in a John Woo flick.

With neither feat, you're at -10/-14.