I believe, and someone correct me if I am wrong, that the 2ohm speakers will either pull more power from the internal amplifier, and it may possibly create to much of a load and overheat the internal amplifier. It could also possibly overpower the speakers and damage them. I'm not an expert, I've just dabbled in a little bit of car stereo, but I think 4ohm speakers are your best bet, but I would double check.
-Zach