Electronic – Power of audio amplifier not matching specifications

I have a Cerwin-Vega CV-2800 audio amplifier which is rated for 600 watts at 8 ohms, 900 watts at 4 ohms, and 1400 watts at 2 ohms. I also have two PWR247T-100-1R00F 1 ohm resistors rated for 100 W; each of these has a measured resistance of 1.2 ohms.

In my first experiment, I wired the amplifier in series with one of the resistors and an inductor which I had wound myself. The inductor has an equivalent series resistance of 1.1 ohms and an inductance of about 3 mH at a frequency of 50 Hz. (The inductance was calculated using the method shown here under the section "Measuring with a sinewave"; I found the phase angle between \$V_x\$ and \$V_g\$ to be \$-20.56\$ degrees.) The circuit is diagrammed below:

^{simulate this circuit – Schematic created using CircuitLab}

I fed in a 50 Hz sinusoidal signal, and turned amplifier up until right before the -20 dB light came on. At this frequency, the reactance of the inductor should be \$\omega L = 2\pi(50)(0.003) = 0.94\$ ohms, so the total impedance of the circuit should be \$\sqrt{(1.2 + 1.1)^2 + (0.94^2)} = 2.49\$ ohms. I measured the voltage across the resistor, the inductor, and the entire circuit and found them to be 4.07 V, 6.2 V, and 9.275 V in amplitude, respectively. I calculated the power consumed by the circuit and found it to be

$$
\begin{align}
P &= IV\\
&= (V_{R_1}/R_1)V_{\mbox{total}}\\
&= (4.07/1.2)(9.275)\\
&= 31.46 \mbox{ watts}
\end{align}
$$

This was much lower than the wattage that the amplifier was rated for, so to determine whether it was something to do with the inductor, I made the load purely resistive. In a second experiment, I wired two of the PWR247T-100-1R00F 1 ohm resistors in series and connected them in series with the amplifier (no inductor at all). The circuit is diagrammed below:

^{simulate this circuit}

I measured the voltage across the entire circuit and found it to be 9.2 V in amplitude. I calculated the peak power using this voltage and found it to be

$$
\begin{align}
P &= V^2/(R_1 + R_2) \\
&= 9.2^2/(1.2 + 1.2) \\
&= 35.27 \mbox{ watts}
\end{align}
$$

Both of these are much less than the 1400 W that the amplifier is rated for. What is the reason for the difference?

Edit: Some comments suggested that because I was not measuring the voltage right before clipping, I was not calculating maximum power correctly. This is true, but I did drive the amplifier once until it started to clip and remember the voltage not exceeding 15 V, about 50% more than the 9.7 V it reaches at the -20 dB point (can verify these numbers in a few hours). This is still only about 100 W of power.

Edit: The voltage clipped because I was looking at it on a NI-DAQ whose range is -10 V to +10 V. See my answer below.