What happens to an amp below 2 ohms?

It depends on the amp. What is the particular amp you have been reading about?

The lower the impedance, the more current the speaker tries to draw from the amp.

With transistor amps, this will certainly result in more heat as the current has to come through the output transistors, even if the amp is class D. Some SS amps have enough current rating in their output sections to support this and others do not.

Tube amps will not produce any more current at all- usually they will put out less power as a result, although with a set of ZEROs http://www.zeroimpedance.com installed, they may be just fine.

Now for the *effects* of a low impedance like that (IOW: the bad news). No matter what kind of amplifier you have, if sound quality is your goal, it will be at a disadvantage driving a load like this, even if the amp has the current to do it. OTOH if *sound pressure* is valued over sound quality, then this *might* be OK, but if that is the case you are often better off seeking a speaker that is higher efficiency that might be a little easier on the amp.

The reason SS amps don't sound their best into lower impedances has to do with internal capacitances that exist in the junctions of the output devices. In most cases, this capacitive element is non-linear. It is magnified by increasing the current through the device- precisely what happens when you use a lower impedance load. This results in greater odd-ordered harmonic distortion, making the amp sound harsher and less transparent.

If you prefer a smoother, more transparent sound then you will find this a good argument to seek a speaker that has a higher impedance.

Another way to look at it is to search for the few, underline few, amps that can comfortably and reliably,heavily underline reliably, drive the Apogee Scintilla which goes down to 1 ohm. Looking at those amps will tell you what is necessary for an amp to handle such a load.

Very few amps will handle such a load but I know of only 2 speakers myself that go below one ohm: the aforementioned Scintilla and the Quad 57. The latter does this in the top end so is not nearly as difficult a load to drive as the Apogee. In a perfect world the impedence curve would stay above 6 ohms but in our world some very good speakers have difficult curves. My Gamut L5s go down to 3.2 or so and my friends Sasha to below 3. The amount of work my CJ 350 has to do driving the Gamuts is considerable, gets quite hot driving them to a good volume in a long session. On the other hand it gets barely warm driving my Spendor S 100s to a similar volume. A good reason why you should always buy the speaker first; then you know what your amp requirements will be.

The Krell KSA and MDA are noted for playing the Apogee line of speakers with aplomb. In fact Krell put themselves on the map by building amps that could do this and were the amps of choice for Apogee to demo with. I'm not sure if some of the latter Krells could still do this but I'd be surprised if they couldn't.