How To Measure "Current" In An Amplifier?

Atmasphere, forgive me but I'm still confused:-). Are you saying for instance that:
a ss amp rated as 100 Watts into 8 Ohms = 200 Watts into 4 Ohms and 50 Watts into 16 Ohms.
and
a tube amp rated as 100 Watts into 8 Ohms = 100 Watts into 4 Ohms and 50 Watts into 16 Ohms.
and that's why tube amps are more expensive?

Using the previously posted example (fig.4):
http://www.stereophile.com/content/conrad-johnson-lp125m-monoblock-power-amplifier-measurements#xxGh...
adds to the confusion.

Very high Damping Factor doesn't make much sense since most of the speaker's impedance is resistive.  For 8 ohm speaker it would be about 6 ohms.  This resistance limits actual DF to 1.3
In order to prevent amp from making it worse 0.8 ohm output impedance would be fine (10% change).

Max current specification may suggest amplifier current limit but it doesn't specify the load impedance and doesn't say what happens with supply voltage.  Even amplifier with very weak power supply might be able to deliver high momentary short circuit current.
AFAIK speaker impedance usually dips around few hundred hertz (first crossover frequency).  Music on the other hand carries the biggest voltage peaks at the lowest frequencies.

@almarg and @atmasphere

These reviews indicate the Musical Fidelity can do 440 watts into 4 ohms and 800 watts into 2 ohms. I’m not stating that is or is not true, but IF true, would that support the 45 peak-to-peak amperage claim (or the RMS conversion to 15.9)? And, to the point of this thread, that it can "easily" drive a low impedance speaker?

http://www.goodsound.com/index.php/component/content/article?id=153:m

http://www.stereofil.no/stereo/integrerte-forsterkere/musical-fidelity-m6si

Gdhal 9-26-16
Atmasphere:  "Regarding your amplifier, the specs don’t add up as presented so there is more to the story. The 45 amp figure seems to refer to output. Converted to RMS as Al did (so it makes more sense) the 15.9amps does not gel with 220 watts. Into 8 ohms at 220 watts the current is 5.24 amps. The 15.9 amp figure makes more sense if the load impedance is slightly less than 3 ohms. At this point the amp would be making a bit over 660 watts. Does that sound right to you? "

I agree at face value the numbers don’t add up. I have sent a question to Musical Fidelity, but wouldn’t hold my breath for a response.

Not sure if it answers Ralph's question, but FWIW it appears that the 220 watt capability of the amp into 8 ohms is voltage limited, not current limited (or thermally limited, for that matter).  The manual indicates that the max output voltage at the onset of clipping, across the 20 Hz to 20 kHz frequency range, is 42 volts RMS, which corresponds almost exactly to 220 watts into 8 ohms.

Best regards,
-- Al