I should clarify, I'm most concerned about the HU, being rated for 4 ohm speakers, getting messed up because the factory amp/drivers are at 2 ohms.

I've got a JVC KD-G430 head unit which I just installed into my '03 Vibe with the M&T package. Didn't realize it had that 200w 2 ohm amp. Now, a friend of mine who's far more well-versed in the car audio department says there's a bit of an issue because the head unit ouptuts are rated for 4 ohm ...