Carver M1.0t vs NAD 2200PE

So I have a HK3380 which I use as a preamp The volume control goes from -80 to +10db. I am currently driving a pair of Polk Audio LSI15 which are 4 ohms.

When the NAD 2200PE (200wpc @ 4 ohms .03% THD) is the playing amp, it plays loud at the volume -25db but will start to clip at -20 to -15db with slight distortion.

As for the Carver M1.0t (400wpc @ 4 ohms .15% THD), to match the volume of the NAD at -25, I have to turn the volume to -10 on the Carver. But the thing is the Carver can be pushed to +5 without any clipping and no distortion.

Does the NAD have more power/reserve because it can play louder at the lower db volume setting or it can pull more power from the wall socket?
Is the Carver more efficient or has more headroom since it can be push well beyond the 0db mark?

It would help for me to understand what exactly to look for determining power and drive. Thanks.
The results have little to do with what you write as the 'reasons'
The amps have different designs, and different gain.
Perhas different input sensitivities and impedance.

The correlation of your volume knob and the areas you ask about.. there is no correlation that matters to the end result you want to know.
The way to see if one uses more A/C watts is to actually measure it.
Most SS amps of that sort have about the same efficiency (give or take some)
One way yu COULD see which is better would be to use an independent Db meter, like a Radio Shack model
(find still available on eBay. or other models on Amazon)
Then you could have an independent level control(using the meter) and know which amp is able to play louder without distortion.
You may be able to tell without the meter. Just which one plays louder without distortion.. It has nothing to do with the volume knob numbers.. And does one sound better when playing at very soft volumes. regarless of the volume knob numbers. Play each at the softest you can hear.. does one seem to be clearer?
Anyway,, hope this helps.
Then one that sounds better IS better.
Thanks for the response, it make it much clearer now.