What happens to an amp below 2 ohms?

Buy amp and speakers as a unit...and than after a nice test listen. If you are really after a 2 ohm stable amp, and they are few/farbetween, leave out ALL the 'd' amps with ICE modules. The data sheet says the limit is 2.7 ohms. I'd be inclined to listen to 'em.

I'm not even gonna touch the 'need' for a 2 ohm speaker. What I will say, is that if it were pure resistive, you'd have better luck. Since it isn't, you have to deal with reactance. bad juju. You may get lucky and it won't be too awful, but in more extreme cases of large phse angles (highly capactivie or inductive) you're gonna suck up amp power like you own stock in the power company.

Hi sensitivity would also help, but only so much. Less phase shift would buy you more than a sheerly high sensitivity number. especially if you knew such phase shift peaked at or near the impedance minima.

In general, however, there's no need for such a wacky load.

Phase is simply put, Power Factor. Another measure of reactance.
The larger the phase angle, the less power delivered to the load. A 1000 watt amp trying to drive a load which has a 90` phase angle will deliver exactly ZERO power at that frequency. cosine 90=0
A speaker which is a difficult load would, IMO, have large phase angles at the same frequencies where impedance dips occur. A double whammy.
My panels? Not a bad load, at all. low impedance, to be sure, but no wacky phase angles to suck up amp power.