Class A bias, speaker sensitivity, watts...?

Depends how far you are measuring at and whether your iPhone’s DB scale is reliable, but probably. Sensitivity is rated at 1 meter, so you should make sure to measure around that distance.

You’d be amazed how little power most of us actually use while listening.

If you want to be sure, get a 60 Hz test tone and an AC capable multimeter. Turn turn the volume up slowly until you measure 2.83 V AC at the speaker input. That’s 1 Watt at 8 or 2 Watts at 4 Ohms.

Also, if you are playing in stereo you'll get a 6 dB bump.  That is, if you put out 2.83V into 2 speakers you'll measure 6dB more than into 1 speaker.

Both speakers playing, distance is just shy of 2 meters

Take away another 6 dB for doubling the distance.

Were you doing the test with a pure tone input, or listening to music?

Just music. "Turn turn the volume up slowly until you measure 2.83 V AC at the speaker input" as in the speaker terminals on the speaker? Or should it be at the speaker tap on the amp?

I'll tell you what I think I know and someone can correct me.  Class A watts approximately halve from 8 ohms into 4 ohms, so you have between 5 and 10 watts of class A power. 

Accuphase does the calculation of watts being output at any given time, but they say the calculation is complex.  Here is their explanation:

Indicates the True Power into the Speaker

The power into the speaker is the product of the amplifier’s output voltage (V) and the current (I); that is, W = V×I. While the voltage is easily measured with a voltmeter, the measurement of current is more complex. Typical power meters avoid this complexity by assuming that the load resistance is equivalent to the speaker's nominal impedance. For these meters, then, I = V/R, and therefore, W = V×V/R, and so W = V2 /R. But as Figure 1 clearly shows, the actual impedance of the speaker varies complexly according to the frequency. The load resistance changes considerably as the impedance moves from peaks to dips, causing the power to change as well. Because typical meters measure only the voltage, they are unable to calculate true power at any given time. The A-80 meter, in contrast. uses detection circuitry, installed at the outputs, to dynamically detect both the load voltage and the current. The meter converts these analog readings into digital values that are then used to calculate the power. It can therefore display the true power value even as the power fluctuates along with the impedance

They have a microprocessor in their amps do the calculation. 

Just a guess, but I think that in a small office with 80 db peaks you would stay in class A watts most of the time and probably wouldn't notice if you went into class B watts.