Sony HT-SS2000 Receiver/Amplifier Questions

[PrecisionAudio]

I am quite certain that this friend's Sony HT-SS2000 Receiver/Amplifier is all Class D due to its very small size.

My questions are about its purported claims for 2-channel amplification and then surround sound amplification. I am not a surround sound kind of guy and rather prefer two excellent mains and two excellent subs for when I am in the so-called "home theater" mode. I guess if I could afford more, I would purchase the other speakers but I am always quality over quantity. I like music and not A/V so much. I am not much into movies.

Here are some of my friend's Sony unit's specifications:

Stereo Mode (aka 2.1):
84W + 84W (into 3 ohms at 170-20,000Hz with a THD of 1.0%)

I am assuming that the subwoofer when in "Stereo Mode" gets the same power as below when in "Surround Mode" which would be 285W (into 1.5 ohms at 80 Hz with a THD of 10.0%) but the manual does not clearly state this. I assume this because the L, R, and SW icons are lit-up when in "Stereo Mode." The sub is powered via the amp and not via an AC plug-in that goes into a plate amp (where the sub would receive only low-level inputs).

Surround Mode (aka 5.1):
Fronts: 143 W/ch (into 3 ohms at 1kHz with THD of 10.0%)
Center: 143 W (into 3 ohms at 1kHz with THD of 10.0%)
Surrounds: 143 W/ch (into 3 ohms at 1kHz with THD of 10.0%)
Subwoofer: 285 W (into 1.5 ohms at 80 Hz with THD of 10.0%)

Is this HT-in-a-box amplifier configuration kind of "standard" nowadays? With the stereo mode having cleaner power but the surround mode having more power but more distortion also?

Also, I have now seen amps range in THD from 10.0% to 1.0% to 0.08% to 0.03%. What is the THD threshold for a very sonically knowledgeable person to notice? I can pick up very small dB variations across a spectrum when using program material that I know extremely well. But, THD, I don't know what I'm looking (listening) for.

Thanks!