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

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.

Yes, you will be operating in class A

Both speakers playing, distance is just shy of 2 meters

Hello Craigvmn. All the numbers can be intimidating, especially when newer, younger writers, with no real knowledge and eager to please their bosses, write rubbish with is filled with pure rubbish and misuse of technical terms. For instance, many preamps are being advertised as Class A. All preamps are Class A. This means the output devices produce a faithful replica of the input, only larger in some way. Other classes of amplification produce altered, non accurate versions of the input. Class B uses two (or more - an even number) outpur devices one producing an enlarged version of the positive going part of the input. enlarged, and the othe  the negative going portion of the input, suitably enlarged. These two get added together and fed to the output device, usually a speaker. The advantage is: less power gets wasted and two output devices can produce four times the output power compared to what one of the output devices could produce on its own, by itself. Class AB (there are several forms) is a combination which produces less inherent distortion than Class B. There is a Class C which is used in radio tranmitters. Class D is another animal entirely and not worth discussing here. 

You have purchased very good merchndise and may be suprised to hear that sound is a very odd form of energy. We humans can hear a mosquito flying in a room several feet away, a very small amount of power. Standing at Niagra Falls, the falling wter creates a great deal of sound energy. It vibrates our clothes, but it doesn't kill us. We hear on a logrithmic scale (spelling may be off). Most people can barely detect an increase in loudness of 3 db. An increase of 6 db is not difficult to notice, but is small. That 6 db represents 4X the power of the sound. A 10 db increase requires 10 times increas of power, but it doesn't sound much louder. As a result, most people don't use much power. Only when the drums go BOOM does the amp need to do serious work. Engoy the music!  You are not likely to heart any distortion in your listening situation. Relax, life is too short to waste on worrying.

Handy test tones but not to tap your toes by. 

http://open.qobuz.com/album/dcon58qby5yxc

http://open.qobuz.com/album/a9odg1f4vqpba

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?

Measuring true RMS voltage with musical signal is generally beyond the ability of a multimeter. That's why @erik_squires was recommending a 60 Hz test tone.

The difference between voltage at the speaker terminal and the speaker tap on the amp is whatever loss is incurred on the speaker cable, which should be small if you are using anything like a normal cable section and length. In any case, considering what you are trying to do, I would measure at the speaker.