I have the impression that amps which double into 4 ohm, have zero negative feedback and have high idle power consumption are the best for high current low volume performance.Actually what you're looking for is the right distortion signature. If the amp has that then the way the amp does it is unimportant. What you're looking for is an amp with a significant 2nd and 3rd harmonic, enough so that the higher orders are masked. This will cause the amp to sound smooth and if the amp is also fairly low in distortion, detailed as well. So you can't see this in the THD figures- you have to see a spectrum of the distortion components.
Also the distortion should be the same at all frequencies. Usually amps are tested for distortion at 100Hz, which isn't high enough to show what's going on. It should have the same THD at 100Hz, 1KHz and 10KHz.
You're probably looking for a solid state amp since your speakers are difficult to drive. You might want to keep in mind that making an amplifier work hard for a living will in all amplifiers cause the amp to make more distortion. Do not be fooled by claims that the difference is 'inaudible' or 'negligible'. It is easily heard as reduced detail and usually harsher and brighter. If you really want to hear what the snare and cymbals are doing, this is an important consideration.
Another issue with inefficient speakers is thermal compression in the voice coils. This is caused by heating of the voice coil with each bass note- it causes the voice coil to become harder to drive and if you simple turn up the volume to try to overcome the dynamic issue this imposes it gets worse. So you might consider getting a speaker that's easier to drive if you really want to hear what the drums are doing.