how does current work in an amplifier?

The KISS answer to your second question is YES. An amplifier rated for a continuous 4 ohm load should handle 4 ohm nominal speakers better than an amplifier that is only rated for a continuous 6 ohm load. You're probably safe to make comparisons within a brand, but I don't think advertised specs really mean much when comparing different brands.

Looking at the question from an 'ohms law' perspective, it is a red herring question.
Even my (alleged) current hungry Magnepans have only a 4 amp fuse on the mid / tweets. Say the low is good for 6 amps.....so the speaker can take a total of 10 amps.
I2R=watts.....so 10*10*5=500 watts at about 5 ohms. That's about it.
Well, the other way to go about it is to MEASURE your speaker. I stuck a DVM on my panels......About 8vac was about the highest value I saw flicker by. Say I double that to 16vac. Since Watts=E2/R That gives me just over 50 watts.
I'll give everyone the benefit of the doubt and double that twice for 200 watts per channel into my panels.
That, sir, is loud....no LOUDER
That is why my opinion, strongly held is that amp amps while not meaningless sure depend on the ability of it to drive those amps at a reasonable voltage to provide POWER.

Don't forget the SOR of a semiconductor. Safe Operating Range. You'd need a real bunch of 'em to sustain 50 amps at 50 volts..........=2500 watts.

Hi Magfan, I believe your DVM is giving you an average RMS voltage reading. It's response is not fast enough show you peak values. Also, if you were playing a sine wave, only then would it be an accurate RMS voltage reading. An oscilloscope is the only accurate way to look at peak voltage/power. Speakers are motors, not resistors. So they have impendance due to back EMF, not really pure resistance. The music signal is AC and so Phase Angle is part of the Impendance/Power Factor. On top of that, the crossovers play into the impedance and phase angle too. So you can see how things get really complicated from a math perspective.

The are some misconceptions about current. Here's the big one:

http://www.atma-sphere.com/papers/myth.html

Others have already touched on the serious aspect of this, the idea that for 200 watts you need 7.07 amps (if a 4 ohm load) which is not really all that much.

Another way of stating 'high current amplifier' is to say that it behaves as a nearly perfect voltage source. Confusing?? yeah. Here's how it works: if the amp makes 28 volts into 8 ohms, that is 98 watts. Now if it is a 'voltage source' it will make the same voltage into 4 ohms and that is double the power, since the current increases as the impedance decreases.

The *real* issue is, is this behavior correct for a panel speaker? For certain box speakers it certainly is, as there is a woofer in the box that has a resonant frequency and that is represented by an impedance peak. With a 'voltage source' amp, that would cause the amp to throttle back its overall power as it encounters the peak. This keeps the frequency response flat.

So is this the right response for a flat panel? The panel has an impedance curve that has nothing to do with a box, and it does have cancellation as you approach the low frequency cutoff. You might want more power, if anything, as you approach the cutoff, to maintain flat response.

Tricky.

This might be why there are so many advocates of tube amps on Magnaplanars; A tube amplifier will try to make something more like constant power into a load rather than constant voltage. This means the voltage and the current will vary with the load.

IME you don't need all that much current to make Magnaplanars sing, the amp just has to be comfortable with the load, which is not that hard. Otherwise they are fairly easy to drive.