Even if you run actives there is strong possibility the speakers reft to right channels will not measure the same in the listening position. My interest is about the inherent noise of these devices mostly
You know most of the reviews back in the day use to quote that ATC are too revealing because of the studio character therefore not ideal for home use...
A bit better maybe but not miles better as you guys say. Actives' amps are usually higher noise designs compared to the best amplification these days although ATC amps are among the best from what i gather.
That is an easy fix IF the actual response has an audible dip in that region or else there is nothing wrong there. The main problem as you see is the tweeter level which is audible.
Source direct applies to all of your inputs and shortens the path for a cleaner signal. It is supposed to have better than 110 db A weighted S/N if the parts are still up to spec.
The specs of your amp are quite good and there is also a direct input where you can use it as a power amp. If you can not hear any hiss with the volume maxed it is probably a good amp. Class d amps have their problems too so dont worry too much.